UNITED STATES              ----------------------------
             SECURITIES AND EXCHANGE COMMISSION   |        OMB APPROVAL        |
                  Washington, DC 20549            |----------------------------|
                                                  |OMB Number:    3235-0059    |
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                                                   ----------------------------

                                  SCHEDULE 14A

           Proxy Statement Pursuant to Section 14(a) of the Securities
                      Exchange Act of 1934 (Amendment No. )


Filed by the Registrant  [X]
Filed by a Party other than the Registrant  [   ]

Check the appropriate box:

[X]  Preliminary Proxy Statement
[ ]  Confidential, for Use of the Commission Only
     (as permitted by Rule 14a-6(e)(2))
[ ]  Definitive Proxy Statement
[ ]  Definitive Additional Materials
[ ]  Soliciting Material Pursuant to Sec. 240.14a-11(c) or Sec. 240.14a-12


                          BARON INVESTMENT FUNDS TRUST
                            (f/k/a Baron Asset Fund)
- --------------------------------------------------------------------------------
                (Name of Registrant as Specified In Its Charter)

- --------------------------------------------------------------------------------
    (Name of Person(s) Filing Proxy Statement if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

[X]  No fee required.

[ ]  Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

     1)   Title of each class of securities to which transaction applies:

- --------------------------------------------------------------------------------
     2)   Aggregate number of securities to which transaction applies:

- --------------------------------------------------------------------------------
     3)   Per unit price or other underlying value of transaction computed
          pursuant to Exchange Act Rule 0-11 (Set forth the amount on which
          the filing fee is calculated and state how it was determined):

- --------------------------------------------------------------------------------
     4)   Proposed maximum aggregate value of transaction:

- --------------------------------------------------------------------------------
     5)   Total fee paid:

- --------------------------------------------------------------------------------

               Persons who are to respond to the collection of information
               contained in this form are not required to respond unless the
               form displays a currently valid OMB control number.

SEC 1913 (04-05)


[ ]  Fee paid previously with preliminary materials.

[ ]  Check box if any part of the is offset as provided  by Exchange  Act Rule
     0-11(a)(2)  and identify the filing for which the  offsetting  fee was paid
     previously.  Identify the previous filing by registration statement number,
     or the Form or Schedule and the date of its filing.

     1)   Amount Previously Paid:

- --------------------------------------------------------------------------------
     2)   Form, Schedule or Registration Statement No.:

- --------------------------------------------------------------------------------
     3)   Filing Party:

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     4)   Date Filed:

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                                                          SEPTEMBER   2006


                                 PROXY STATEMENT




                            [registered castle logo]

                                  B  A  R  O  N
                                  F  U  N  D  S(r)







                                        >  BARON ASSET FUND



Enclosed is a Proxy  Statement  and Proxy  Voting Card for  shareholders  of the
Baron Asset Fund series.

We are asking you to vote on the following item:


CONVERSION  OF BARON ASSET FUND FROM A SMALL AND MID-CAP FUND TO A MID-CAP FUND.
We are proposing to change the investment  goal of Baron Asset Fund to allow the
Fund to invest  principally in mid-sized growth companies,  which are defined as
having a market capitalization of between $2.5 billion and $8 billion.

Please read the enclosed Proxy  Statement  carefully and please cast your votes,
either electronically, by telephone, or by marking the proxy card and mailing it
to us. Every vote is important to us.

Thank you.



                                BARON ASSET FUND

                            ------------------------

                    Notice of Special Meeting of Shareholders

                            ------------------------


To Our Shareholders:

     Please take notice that a Special Meeting of  Shareholders  (the "Meeting")
of Baron Asset Fund (the  "Fund")  which is a series of Baron  Investment  Funds
Trust (f/k/a Baron Asset Fund),  a  Massachusetts  business trust (the "Trust"),
will be held on  December  5,  2006 at 11:00  a.m.  eastern  time.  Please  call
1-800-992-2766 should you require additional information regarding the Meeting.

     The shareholders of the Fund will be asked to consider and vote together as
a single class on the following proposal, which is described in the accompanying
proxy statement:

     (1)  To  approve  or  disapprove  a change  to the  investment  goal of the
          Fund.

     The  shareholders of the Fund will be asked to consider and vote separately
on  the  following  proposal,  which  is  described  in the  accompanying  proxy
statement:

     (2)  To  transact  such other  business  as may  properly  come  before the
          Special Meeting of Shareholders or any adjournment thereof.

     Only  holders of record of shares of common  stock of the Fund at the close
of business on October 6, 2006,  are  entitled to vote at the Meeting and at any
adjournments thereof.

     THE BOARD OF TRUSTEES  UNANIMOUSLY  RECOMMENDS THAT SHAREHOLDERS VOTE "FOR"
THE PROPOSAL.

     In the event that the necessary quorum to transact business, or if the vote
required to approve a proposal is not obtained at the Meeting, the persons named
on the  proxy  card as  proxies  may  propose  one or more  adjournments  of the
Meeting,  in accordance with  applicable law, to permit further  solicitation of
proxies.  Any such  adjournment will require the affirmative vote of the holders
of a majority of the Fund's shares present in person or by proxy at the Meeting.
The  persons  named as  proxies  will  vote in favor of such  adjournment  those
proxies  which they are  entitled to vote in favor of the proposal and will vote
against any such adjournment those proxies to be voted against the proposal.

                                      -1-



                         By order of the Board of Trustees,



                         /s/ Linda S. Martinson
                         -----------------------
                             Linda S. Martinson
                             SECRETARY


September 22, 2006



                                      -2-


IMPORTANT

Your vote is important and, as a shareholder, you are asked to be at the Meeting
either in person or by proxy.  If you are unable to attend the meeting in person
we urge you to vote by proxy  since  you can  always  revoke  your  proxy at the
meeting. You can do this by:

     1.   Completing,  signing, dating and promptly returning the enclosed proxy
          card using the enclosed postage prepaid envelope;

     2.   Calling the toll-free number on your proxy card; or

     3.   Voting at the Internet web site on your proxy card.

     YOUR PROMPT  VOTING BY PROXY MAY SAVE THE  NECESSITY AND EXPENSE OF FURTHER
SOLICITATIONS  TO  ENSURE A QUORUM  AT THE  MEETING.  VOTING  BY PROXY  WILL NOT
PREVENT YOU FROM PERSONALLY VOTING YOUR SHARES AT THE MEETING AND YOU MAY REVOKE
YOUR PROXY BY ADVISING  THE  SECRETARY  OF THE TRUST IN WRITING  (BY  SUBSEQUENT
PROXY OR THROUGH THE WEB SITE) OR BY  TELEPHONE OF SUCH  REVOCATION  AT ANY TIME
BEFORE THE MEETING.

                                      -3-


                                BARON ASSET FUND

                          767 Fifth Avenue, 49th Floor
                               New York, NY 10153
                          ----------------------------

                                 PROXY STATEMENT

                          ----------------------------
GENERAL

     This Proxy  Statement is furnished in connection  with the  solicitation of
proxies  by the  Board of  Trustees  (the  "Board")  of Baron  Investment  Funds
Trust(f/k/a  Baron Asset Fund) (the "Trust"),  on behalf of the BARON ASSET FUND
SERIES (the  "Fund).  This proxy  statement  is for use at a Special  Meeting of
Shareholders  (the  "Meeting"),  to be held on  December  5, 2006 at 11:00 a.m.,
eastern  time,   and  at  any  and  all   adjournments   thereof.   Please  call
1-800-992-2766 should you require additional information regarding the Meeting.

     This Proxy Statement,  the Notice of Special  Meeting,  and the proxy cards
are first being mailed to  shareholders on or about October 16, 2006, or as soon
as  practicable  thereafter.  Any  shareholder  giving a proxy  has the power to
revoke it in person at the Meeting,  by mail  (addressed to the Secretary at the
principal office of the Fund, 767 Fifth Avenue, 49th floor, New York, NY 10153),
by  visiting  the  Internet  website on your proxy card,  calling the  toll-free
number on your proxy card, by executing a superseding  proxy, or by submitting a
notice of revocation to the Fund. All properly executed proxies received in time
for the Meeting will be voted as specified in the Proxy Statement.

     Holders  of record of the  shares of the Fund at the close of  business  on
October 6, 2006,  (the "Record Date") will be entitled to one vote per share for
the Fund on all business relevant to that Fund to be conducted at the Meeting.

     A majority of the outstanding  shares must be present in person or by proxy
to constitute a quorum for the transaction of business.  If the necessary quorum
to  transact  business  or the vote  required  to approve  the  proposal  is not
obtained  at the  Meeting,  the  persons  named as proxies on the proxy card may
propose one or more  adjournments of the Meeting,  in accordance with applicable
law, to permit the further  solicitation of proxies.  Any such adjournment would
require  the  affirmative  vote  of a  majority  of  the  shares  voting  on the
adjournment. The persons named as proxies will vote in favor of such adjournment
those proxies which they are entitled to vote in favor of the proposal, and will
vote against any such  adjournment  those proxies that they have been instructed
to vote  against the  proposal.  For purposes of  determining  the presence of a
quorum for the Meeting,  abstentions  will be treated as shares that are present
but which have not been voted. Brokers and other nominees may not be eligible to
vote on certain matters with respect to shares that are not  beneficially  owned
by them  and as to  which  they  have  not  received  voting  instructions;  and
accordingly  these "broker  non-votes" will be disregarded for quorum and voting
purposes  on such  matters.  SHAREHOLDERS  ARE  URGED TO  FORWARD  THEIR  VOTING
INSTRUCTIONS PROMPTLY.

     The Annual  Financial  Report for the Funds of the Trust for the year ended
September  30,  2005,  was mailed to  shareholders  the last week in November of
2005. The unaudited  Semi-Annual Financial Report for the Funds of the Trust was
mailed to  shareholders  in May of 2006.  Both of these reports are available on
the website of the Securities and Exchange  Commission,  www.sec.gov,  under the
name Baron Investment Funds Trust. In addition, copies of these reports are also
available free of charge by calling 1-800-992-2766.

                                      -4-


PROPOSAL
- --------

     SUMMARY

     The  following  proposal is being  submitted  by the Board of Trustees  for
     action at the Meeting.224


     PROPOSAL
     --------

     To amend the investment goal of Baron Asset Fund


     The Board of Trustees asks  shareholders  of Baron Asset Fund to change the
Fund's  investment  goal.  This proposal  requires the  affirmative  vote of the
lesser of: (a) 67% of the Baron Asset Fund series' shares present at the Meeting
if more than 50% of such  shares  outstanding  on the record date are present in
person or by proxy or (b) more than 50% of the  shares of the Baron  Asset  Fund
series' shares outstanding on the record date.

BOARD OF TRUSTEES RECOMMENDATION

     THE BOARD OF  TRUSTEES  OF THE TRUST  RECOMMENDS  THAT YOU VOTE IN FAVOR OF
CHANGING THE FUND'S  INVESTMENT  GOAL. The Fund's current  investment goal is to
achieve  capital  appreciation  through  long-term  investments in securities of
small and medium sized  companies with  undervalued  assets or favorable  growth
prospects.  The Board proposes that the current  investment  goal of the Fund as
set forth above be  replaced  with the  following  investment  goal:  To provide
capital appreciation  through investments  primarily in the securities of medium
sized growth companies.

     During the past five years,  to improve the Fund's  performance  and reduce
its  portfolio  risk,  the  Adviser  has  restructured  the  Fund's   investment
portfolio.  One way the Adviser has accomplished  this is by focusing the Fund's
portfolio,  which currently includes both small and mid-cap growth companies, on
mid-cap  growth  companies  which  the  Adviser  believes  have  continuing  and
significant growth prospects.  The percentage of companies in the portfolio with
market  capitalizations of less than $2.5 billion has fallen from 41.6% to 12.6%
during the past five years.  Today, the Fund is classified by independent rating
agencies as a mid-cap growth fund.

     This shift will allow the Adviser to better distinguish the Fund from Baron
Fund's two small-cap  growth funds,  Baron Growth Fund and Baron Small Cap Fund.
The  Board  believes  this  will  reduce   confusion  among  both  our  existing
shareholders and prospective  investors.  In addition,  these changes will allow
this Fund to take advantage of Baron Funds' increasing  institutional  knowledge
of the many successful small growth companies which have become mid sized growth
companies and which the Adviser  believes  have  significant  growth  prospects.
Medium-sized  growth companies are defined as having a market  capitalization of
between $2.5 billion and $8 billion.

     The Board  believes this change will benefit the Fund's  shareholders.  The
Board  recommends  that you approve the change in  investment  goal to allow the
Fund to invest  principally  in mid-sized  growth  businesses.  If  shareholders
approve this change,  the new  investment  goal would become  effective upon the
effectiveness  of the  amendment  to the Trust's  registration  statement  which
reflects  this  change.  If  shareholders  do not  approve  this  proposal,  the
investment goal will not change.

                                      -5-



REQUIRED VOTE

     Approval of this proposal  requires the affirmative  vote of the lesser of:
(a) 67% of the Baron  Asset Fund  series'  shares  present  at the  Meeting if a
majority  of such  shares are present in person or by proxy or (b) more than 50%
of the outstanding shares of the Baron Asset Fund series' shares. It is intended
that the  enclosed  proxy will be voted for the  proposal  unless  authority  is
withheld in the proxy. THE BOARD OF TRUSTEES RECOMMENDS THAT THE SHAREHOLDERS OF
THE FUND VOTE IN FAVOR OF THIS PROPOSAL.

ADDITIONAL INFORMATION

     The name and address of the  Investment  Adviser is BAMCO,  Inc., 767 Fifth
Avenue,  49th Floor, New York, New York, 10153. The cost of preparing,  printing
and mailing the proxy,  notice and Proxy  Statement and all other costs incurred
in  connection  with the  solicitation  of  proxies,  including  any  additional
solicitation made by letter, telephone or other means, will be paid by the Fund.

     The name and address of the principal  underwriter and distributor is Baron
Capital, Inc., 767 Fifth Avenue, 49th Floor, New York, New York, 10153.

     It is expected that the  solicitation of proxies will be primarily by mail.
A proxy  solicitation  firm may be  engaged  to  assist in the  solicitation  of
proxies. To the extent that votes are not received,  the proxy solicitation firm
may contact  shareholders  by  telephone.  Shareholders  may authorize the proxy
solicitation  firm to execute  proxies on their behalf,  by telephone or through
the  Internet.  Proxies  that are obtained by  telephone  authorization  will be
recorded in accordance with  procedures  that are reasonably  designed to ensure
that  the  identity  of  the  shareholder   casting  the  vote  and  the  voting
instructions of the shareholder are accurately determined.

     When soliciting  telephonic proxies,  the representative is required to ask
for each shareholder's full name, address, social security or tax identification
number,  and the number of shares  owned to  confirm  that the  shareholder  has
received the Proxy  Statement and proxy card in the mail. If the  information is
consistent,  the proxy  solicitor  would  explain  the  voting  process  and the
proposals and ask for the shareholder's voting instructions. The proxy solicitor
would not  recommend  to the  shareholder  how to vote,  other  than to read any
recommendations  set forth in the Proxy Statement.  The proxy  solicitation firm
confirms  the  voting  instructions  to the  shareholder  promptly  by letter or
mailgram.

     Shareholders  who want to vote by electronic proxy rather than mailing back
the proxy card,  may do so by accessing  the Internet  website  indicated on the
proxy card or by calling the toll-free number  referenced on the proxy card. The
shareholder  will be prompted to provide his or her control  number that appears
on the proxy card. If the information is correctly entered, the shareholder will
be provided with instructions,  and the opportunity to enter votes. Confirmation
of telephone voting  instructions are done immediately over the phone, while the
shareholder will be sent electronic  confirmation of the voting  instructions by
e-mail.

     Proxies may also be voted by filling out the proxy card sent with the Proxy
Statement  and  returning  it to  the  Fund.  For  replacement  proxy  cards  or
additional information, please call the Fund at 1- 800-992-2766. Any proxy given
by a shareholder, whether in writing or by telephone, is revocable. Shareholders
may attend the meeting in person.

     There is only one class of shares for the Fund,  and each share is entitled
to one vote. There is no cumulative  voting. At the close of business on October
6, 2006, the record date for  determination  of shareholders  entitled to notice
and to vote at the  Meeting,  the  number of  outstanding  shares of  beneficial
interest for the Fund is                  .

                                      -6-



     As of October 6, 2006,  the record date,  the  following  chart lists those
shareholders who beneficially  owned as much as 5% of the outstanding  shares of
capital  stock of the Fund,  and also shows the  aggregate  holdings  of persons
affiliated with the Fund and the Adviser:



                                BARON ASSET FUND
                                ----------------
NAME OF 5% OWNER**                                 OWNERSHIP PERCENTAGE
- ----------------                                   --------------------

Clients of Charles Schwab & Co., Inc.

Clients of National Financial Services Corp.

- -----
**  Affiliated Persons' (Officers and Trustees) Aggregate Ownership Percentage
    as a group, own less than 1%.


HOUSEHOLDING NOTICE

     To avoid sending  duplicate  copies of materials to households  and thereby
reduce expenses,  only one copy of the most recent annual and semiannual reports
of the Fund may be mailed to shareholders, having the same last name and address
in the  Fund's  records.  The  consolidation  of these  mailings,  householding,
benefits the Fund through reduced mailing expense.  You may call  1-800-992-2766
or  write  to the  Fund at 767  Fifth  Avenue,  New  York,  NY 10153 if you need
additional  copies of the documents,  or if you wish to receive  separate annual
reports or proxy statements in the future. You may also visit www.BaronFunds.com
to view and/or download these documents,  as well as other information about the
Fund.

OTHER MATTERS TO COME BEFORE THE MEETING

     The Board is not aware of any  other  business  to be  brought  before  the
Special Meeting. Should any other matters requiring a shareholder vote arise, it
is the intention that proxies that do not contain  specific  restrictions to the
contrary  will be voted on such matters in  accordance  with the judgment of the
persons named in the enclosed form of proxy.

     SHAREHOLDERS  WHO DO NOT EXPECT TO BE PRESENT AT THE  SPECIAL  MEETING  ARE
URGED TO SIGN AND DATE THE  ENCLOSED  PROXY CARD AND  PROMPTLY  RETURN IT IN THE
ENCLOSED  ENVELOPE WHICH IS ADDRESSED FOR YOUR  CONVENIENCE AND NEEDS NO POSTAGE
IF MAILED IN THE UNITED  STATES OR VOTE BY  TOLL-FREE  TELEPHONE  CALL OR AT THE
WEB-SITE. TO AVOID THE EXPENSE OF FURTHER SOLICITATION, PLEASE VOTE PROMPTLY.

SHAREHOLDER PROPOSALS

     Any  shareholder  proposal to be included  in the proxy  statement  for the
Fund's  next  meeting of  shareholders  must be  received  by the Fund  within a
reasonable  period of time prior to that  meeting.  The Fund is not  required to
hold  annual  meetings  of  shareholders  and  has no  current  plan  to  hold a
shareholder meeting in the next year.

                              By order of the Board of Trustees


                              /s/ Linda S. Martinson
                              ----------------------
                                  Linda S. Martinson
                                  SECRETARY




                                           
[registered      BARON FUNDS                      ---------------------------------------------------------------------------------
castle logo]     P.O. BOX 9132                    |                     THREE EASY WAYS TO VOTE THIS FORM                         |
B A R O N        HINGHAM, MA 02043-9132           |          READ THE PROXY STATEMENT AND HAVE THIS FORM AT HAND.                 |
F U N D S(r)                                      | TELEPHONE: Call 1-800-690-6903 and follow the recorded instructions.          |
                                                  |  INTERNET: Go to www.proxyvote.com and follow the on-screen instructions.     |
                                                  |      MAIL: Check the appropriate box on the reverse side of this Form, sign   |
                                                  |            date below, and return in the postage-paid envelope provided.      |
                                                  |                                                                               |
                                                  |          IF YOU VOTE BY TELEPHONE OR INTERNET, DO NOT MAIL THIS FORM.         |
                                                  ---------------------------------------------------------------------------------

////////////////////
/(control number)  /
///////////////////


BARON ASSET FUND                                                THIS PROXY IS SOLICITED ON BEHALF OF THE TRUSTEES

The undersigned hereby appoints Ronald Baron, President and CEO and Linda Martinson, Vice President, COO, Secretary and General
Counsel, and each of them, attorneys and proxies of the undersigned, with full powers of substitution and revocation, to represent
the undersigned and to vote on behalf of the undersigned all shares of BARON ASSET FUND (the "Fund") which the undersigned is
entitled to vote at a Special Meeting of Shareholders of the Fund to be held on December 5, 2006 at 11:00 a.m. eastern time, and
any adjournments thereof.  Please call 1-800-992-2766 should you require additional information regarding the Meeting.  The
undersigned hereby acknowledges receipt of the Notice of Special Meeting of Shareholders and Proxy Statement and hereby instructs
said attorneys and proxies to vote said shares as indicated herein, in their discretion, the proxies are authorized to vote upon
such other business as may properly come before the Meeting.

Either of the proxies present and acting at the Meeting in person or by substitute shall have and may exercise all of the power and
authority of said proxies hereunder. The undersigned hereby revokes any proxy previously given.

This proxy, if properly executed, will be voted in the manner directed by the undersigned shareholder. If no direction is made as
to any Proposal, this proxy will be voted FOR the Proposal. Please refer to the Proxy Statement for a discussion of each of the
Proposals.

                                                                         PLEASE VOTE, DATE, AND SIGN BELOW
                                                                         ---------------------------------
                                                                              AND RETURN PROMPTLY IN
                                                                              ----------------------
                                                                                ENCLOSED ENVELOPE
                                                                                -----------------

                                                                           Date ---------------------
        [SHAREHOLDER(S) NAME & ADDRESS]                                    -----------------------------------------------------
                                                                           |                                                   |
                                                                           |                                                   |
                                                                           -----------------------------------------------------
                                                                           Shareholder(s) sign here            (SIGN IN THE BOX)

                                                                           Please sign this proxy exactly as your name appears on
                                                                           the books of the Fund. Joint owners should each sign
                                                                           personally. Trustees and other fiduciaries should
                                                                           indicate the capacity in which they sign, and where more
                                                                           than one name appears, a majority must sign. If a
                                                                           corporation, the signature should be that of an
                                                                           authorized officer who should state his or her title.




PLEASE FILL IN BOX(ES) AS SHOWN USING BLACK OR BLUE INK OR NUMBER 2 PENCIL.   [X]
PLEASE DO NOT USE FINE POINT PENS.


1)   To convert Baron Asset Fund from a small and mid-cap fund to a mid-cap fund.                          FOR   AGAINST   ABSTAIN

                                                                                                           [ ]     [ ]       [ ]

- --------------------------------------------------------------------------------------------------------
2)   To transact such other business as may properly come before the Meeting or any adjournment thereof.   FOR   AGAINST   ABSTAIN

                                                                                                           [ ]     [ ]       [ ]

                                    PLEASE BE SURE TO DATE AND SIGN THIS PROXY ON THE REVERSE SIDE.