Exhibit 4

                      AGREEMENT AND PLAN OF REORGANIZATION

     THIS AGREEMENT AND PLAN OF REORGANIZATION (the "Agreement") is made as of
this           day of           , 2006, by and between Janus Investment Fund, a
Massachusetts business trust (the "Trust"), on behalf of Janus Olympus Fund, a
series of the Trust (the "Predecessor Fund"), Janus Orion Fund, a series of the
Trust (the "Successor Fund"), and Janus Capital Management LLC, a Delaware
limited liability company ("JCM").

     All references in this Agreement to action taken by the Predecessor Fund or
the Successor Fund shall be deemed to refer to action taken by the Trust on
behalf of the respective portfolio series.

     This Agreement is intended to be and is adopted as a plan of reorganization
and liquidation within the meaning of Section 368(a) of the United States
Internal Revenue Code of 1986, as amended (the "Code"). The reorganization (the
"Reorganization") will consist of the transfer by the Predecessor Fund of all or
substantially all of its assets to the Successor Fund, in exchange solely for
shares of beneficial interest in the Successor Fund ("New Shares") having a net
asset value equal to the net asset value of the Predecessor Fund, the assumption
by the Successor Fund of all the liabilities of the Predecessor Fund, and the
distribution of the New Shares to the shareholders of the Predecessor Fund in
complete liquidation of the Predecessor Fund as provided herein, all upon the
terms and conditions hereinafter set forth in this Agreement.

     WHEREAS, the Board of Trustees of the Trust has determined that it is in
the best interest of the Predecessor Fund and the Successor Fund, respectively,
that the assets of the Predecessor Fund be acquired by the Successor Fund
pursuant to this Agreement and in accordance with the applicable statutes of the
Commonwealth of Massachusetts and that the interests of existing shareholders
will not be diluted as a result of this transaction;

     NOW, THEREFORE, in consideration of the premises and of the covenants and
agreements hereinafter set forth, the parties hereto covenant and agree as
follows:

1.  PLAN OF REORGANIZATION

     1.1  Subject to the terms and conditions herein set forth, the Trust shall
(i) transfer all or substantially all of the assets of the Predecessor Fund, as
set forth in paragraph 1.2, to the Successor Fund, (ii) cause the Successor Fund
to deliver to the Trust full and fractional New Shares of the Successor Fund,
having a net asset value equal to the value of the net assets of the shares of
the Predecessor Fund as of the close of regular session trading on the New York
Stock Exchange on the Closing Date, as set forth in Article 2 and (iii) assume
all liabilities of the Predecessor

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Fund, as set forth in paragraph 1.2. Such transactions shall take place at the
closing provided for in paragraph 2.1 (the "Closing").

     1.2  The assets of the Predecessor Fund to be acquired by the Successor
Fund shall consist of all property, including, without limitation, all cash,
securities, commodities and futures interests, and dividends or interest
receivable which are owned by the Predecessor Fund and any deferred or prepaid
expenses shown as an asset on the books of the Predecessor Fund on the closing
date provided in paragraph 2.1 (the "Closing Date"). The Successor Fund will
assume all of the liabilities, expenses, costs, charges and reserves of the
Predecessor Fund of any kind, whether absolute, accrued, contingent or otherwise
in existence on the Closing Date.

     1.3  The Predecessor Fund will distribute pro rata to its shareholders of
record, determined as of immediately after the close of business on the Closing
Date (the "Current Shareholders"), the New Shares received by the Trust pursuant
to paragraph 1.1. Such distribution and liquidation will be accomplished by the
transfer of the New Shares then credited to the accounts of the Predecessor Fund
on the books of the Successor Fund to open accounts on the share records of the
Successor Fund in the names of the Current Shareholders and representing the
respective pro rata number of the New Shares due such shareholders. All issued
and outstanding shares of the Predecessor Fund will simultaneously be canceled
on the books of the Trust. The Successor Fund shall not issue certificates
representing the New Shares in connection with such exchange. Ownership of New
Shares will be shown on the books of the Trust's transfer agent. As soon as
practicable after the Closing, the Trust shall take all steps necessary to
effect a complete liquidation of the Predecessor Fund.

2.  CLOSING AND CLOSING DATE

     2.1  The Closing Date shall be October 31, 2006, or such date as the
parties may agree to in writing. All acts taking place at the Closing shall be
deemed to take place simultaneously as of immediately after the close of
business on the Closing Date unless otherwise agreed to by the parties. The
close of business on the Closing Date shall be as of 4:00 p.m. New York Time.
The Closing shall be held at the offices of Janus Capital Management LLC ("Janus
Capital"), 151 Detroit Street, Denver, Colorado 80206, or at such other time
and/or place as the parties may agree.

     2.2  The Trust shall cause Janus Services LLC (the "Transfer Agent"),
transfer agent of the Predecessor Fund, to deliver at the Closing a certificate
of an authorized officer stating that its records contain the names and
addresses of the Current Shareholders and the number and percentage ownership of
outstanding shares of the Predecessor Fund owned by each such shareholder
immediately prior to the Closing. The Successor Fund shall issue and deliver a
confirmation evidencing the New Shares to be credited on the Closing Date to the
Secretary of the Trust or provide evidence satisfactory to the Trust that such
New Shares have been credited to the accounts of the Predecessor Fund on the
books of the Successor
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Fund. At the Closing, each party shall deliver to the other such bills of sales,
checks, assignments, share certificates, if any, receipts or other documents as
such other party or its counsel may reasonably request.

3.  REPRESENTATIONS AND WARRANTIES

     3.1  The Trust, on behalf of the Predecessor Fund, hereby represents and
warrants to the Successor Fund as follows:

          (i) the Trust is a business trust duly organized, validly existing and
     in good standing under the laws of the Commonwealth of Massachusetts and
     has full corporate power and authority to conduct its business as presently
     conducted;

          (ii) the Trust has full power and authority to execute, deliver and
     carry out the terms of this Agreement on behalf of the Predecessor Fund;

          (iii) the execution and delivery of this Agreement on behalf of the
     Predecessor Fund and the consummation of the transactions contemplated
     hereby are duly authorized and no other proceedings on the part of the
     Trust or the shareholders of the Predecessor Fund (other than as
     contemplated in paragraph 4.1(vi)) are necessary to authorize this
     Agreement and the transactions contemplated hereby;

          (iv) this Agreement has been duly executed by the Trust on behalf of
     the Predecessor Fund and constitutes its valid and binding obligation,
     enforceable in accordance with its terms, subject to applicable bankruptcy,
     reorganization, insolvency, moratorium and other rights affecting
     creditors' rights generally, and general equitable principles;

          (v) neither the execution and delivery of this Agreement by the Trust
     on behalf of the Predecessor Fund, nor the consummation by the Trust on
     behalf of the Predecessor Fund of the transactions contemplated hereby,
     will conflict with, result in a breach or violation of or constitute (or
     with notice, lapse of time or both) a breach of or default under, the
     Trust's Amended and Restated Agreement and Declaration of Trust
     ("Declaration of Trust") or By-Laws of the Trust, as each may be amended,
     or any statute, regulation, order, judgment or decree, or any instrument,
     contract or other agreement to which the Trust is a party or by which the
     Trust or any of its assets is subject or bound; and

          (vi) the unaudited statement of assets and liabilities of the
     Predecessor Fund as of the Closing Date, determined in accordance with
     generally accepted accounting principles consistently applied from the
     prior audited period, accurately reflects all liabilities of the
     Predecessor Fund as of the Closing Date; and

          (vii) no authorization, consent or approval of any governmental or
     other public body or authority or any other party is necessary (other than
     as contemplated in paragraph 4.1(vi)) for the execution and delivery of
     this
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     Agreement by the Trust on behalf of the Predecessor Fund or the
     consummation of any transactions contemplated hereby by the Trust, other
     than as shall be obtained at or prior to the Closing.

     3.2  The Trust, on behalf of the Successor Fund, hereby represents and
warrants to the Predecessor Fund as follows:

          (i) the Trust is a business trust duly organized, validly existing and
     in good standing under the laws of the Commonwealth of Massachusetts and
     has full corporate power and authority to conduct its business as presently
     conducted;

          (ii) the Trust has full power and authority to execute, deliver and
     carry out the terms of this Agreement on behalf of the Successor Fund;

          (iii) the execution and delivery of this Agreement on behalf of the
     Successor Fund and the consummation of the transactions contemplated hereby
     are duly authorized and no other proceedings on the part of the Trust or
     the shareholders of the Successor Fund are necessary to authorize this
     Agreement and the transactions contemplated hereby;

          (iv) this Agreement has been duly executed by the Trust on behalf of
     the Successor Fund and constitutes its valid and binding obligation,
     enforceable in accordance with its terms, subject to applicable bankruptcy,
     reorganization, insolvency, moratorium and other rights affecting
     creditors' rights generally, and general equitable principles;

          (v) neither the execution and delivery of this Agreement by the Trust
     on behalf of the Successor Fund, nor the consummation by the Trust on
     behalf of the Successor Fund of the transactions contemplated hereby, will
     conflict with, result in a breach or violation of or constitute (or with
     notice, lapse of time or both constitute) a breach of or default under, the
     Declaration of Trust or By-Laws of the Trust, as each may be amended, or
     any statute, regulation, order, judgment or decree, or any instrument,
     contract or other agreement to which the Trust is a party or by which the
     Trust or any of its assets is subject or bound; and

          (vi) the net asset value per share of the Successor Fund as of the
     close of regular session trading on the New York Stock Exchange on the
     Closing Date reflects all liabilities of the Successor Fund as of that time
     and date; and

          (vii) no authorization, consent or approval of any governmental or
     other public body or authority or any other party is necessary for the
     execution and delivery of this Agreement by the Trust on behalf of the
     Successor Fund or the consummation of any transactions contemplated hereby
     by the Trust, other than as shall be obtained at or prior to the Closing.

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4.  CONDITIONS PRECEDENT

     4.1  The obligations of the Trust on behalf of each of the Predecessor Fund
and the Successor Fund to effectuate the Reorganization shall be subject to the
satisfaction of the following conditions:

          (i) The Trust shall have filed with the Securities and Exchange
     Commission (the "Commission") a registration statement on Form N-14 under
     the Securities Act of 1933, as amended (the "Securities Act") and such
     amendment or amendments thereto as are determined by the Board of Trustees
     of the Trust to be necessary and appropriate to effect the registration of
     the New Shares (the "Registration Statement"), and the Registration
     Statement shall have become effective, and no stop-order suspending the
     effectiveness of the Registration Statement shall have been issued, and no
     proceeding for that purpose shall have been initiated or threatened by the
     Commission (and not withdrawn or terminated);

          (ii) The applicable New Shares shall have been duly qualified for
     offering to the public in all states in which such qualification is
     required for consummation of the transactions contemplated hereunder;

          (iii) All representations and warranties of the Trust on behalf of the
     Predecessor Fund contained in this Agreement shall be true and correct in
     all material respects as of the date hereof and as of the Closing, with the
     same force and effect as if then made, and the Trust on behalf of the
     Successor Fund shall have received a certificate of an officer of the Trust
     acting on behalf of the Predecessor Fund to that effect in form and
     substance reasonably satisfactory to the Trust on behalf of the Successor
     Fund;

          (iv) All representations and warranties of the Trust on behalf of the
     Successor Fund contained in this Agreement shall be true and correct in all
     material respects as of the date hereof and as of the Closing, with the
     same force and effect as if then made, and the Trust on behalf of the
     Predecessor Fund shall have received a certificate of an officer of the
     Trust acting on behalf of the Successor Fund to that effect in form and
     substance reasonably satisfactory to the Trust on behalf of the Predecessor
     Fund;

          (v) The Trust on behalf of the Predecessor Fund and the Successor Fund
     shall have received a favorable opinion of Goodwin Procter LLP satisfactory
     to counsel for the Trust, to the effect that, for federal income tax
     purposes:

             (a) The acquisition by the Successor Fund of the assets of the
        Predecessor Fund in exchange for the Successor Fund's assumption of the
        liabilities of the Predecessor Fund and issuance of the New Shares,
        followed by the distribution by the Predecessor Fund of such the New
        Shares to the shareholders of the Predecessor Fund in exchange for their
        shares of the Predecessor Fund, all as provided in paragraph 1 hereof,
        will constitute a reorganization within the meaning of Section 368(a) of
        the

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        Code, and the Predecessor Fund and the Successor Fund will each be "a
        party to a reorganization" within the meaning of Section 368(b) of the
        Code;

             (b) No gain or loss will be recognized to the Predecessor Fund (i)
        upon the transfer of its assets to the Successor Fund in exchange for
        the New Shares or (ii) upon the distribution of the New Shares to the
        shareholders of the Predecessor Fund as contemplated in paragraph 1
        hereof;

             (c) No gain or loss will be recognized to the Successor Fund upon
        the receipt of the assets of the Predecessor Fund in exchange for the
        assumption of liabilities and Obligations and issuance of the New Shares
        as contemplated in paragraph 1 hereof;

             (d) The tax basis of the assets of the Predecessor Fund acquired by
        the Successor Fund will be the same as the basis of those assets in the
        hands of the Predecessor Fund immediately prior to the transfer, and the
        holding period of the assets of the Predecessor Fund in the hands of the
        Successor Fund will include the period during which those assets were
        held by the Predecessor Fund;

             (e) The shareholders of the Predecessor Fund will recognize no gain
        or loss upon the exchange of all of their shares of the Predecessor Fund
        for the New Shares;

             (f) The tax basis of the New Shares to be received by each
        shareholder of the Predecessor Fund will be the same in the aggregate as
        the aggregate tax basis of the shares of the Predecessor Fund
        surrendered in exchange therefor;

             (g) The holding period of the New Shares to be received by the
        shareholders of the Predecessor Fund will include the period during
        which the shares of the Predecessor Fund surrendered in exchange
        therefor were held, provided such shares of the Predecessor Fund were
        held as a capital asset on the date of the exchange.

             (h) Successor Fund will succeed to and take into account the items
        of Predecessor Fund described in Section 381(c) of the Code, subject to
        the conditions and limitations specified in Sections 381, 382, 383 and
        384 of the Code and the regulations thereunder.

          (vi) The shareholders of the Predecessor Fund shall have approved this
     Agreement and Plan of Reorganization at a special meeting of the
     shareholders of the Predecessor Fund.

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5.  EXPENSES

     All of the expenses and costs of the Reorganization and the transactions
contemplated thereby shall be borne by Janus Capital.

6.  ENTIRE AGREEMENT

     The Trust agrees on behalf of each of the Predecessor Fund and the
Successor Fund that this Agreement constitutes the entire agreement between the
parties.

7.  TERMINATION

     This Agreement and the transactions contemplated hereby may be terminated
and abandoned by resolution of the Board of Trustees of the Trust, at any time
prior to the Closing Date, if circumstances should develop that, in the opinion
of the Board of Trustees, make proceeding with the Agreement inadvisable.

8.  AMENDMENTS

     This agreement may be amended, modified or supplemented in such manner as
may be mutually agreed upon in writing by the parties.

9.  NOTICES

     Any notice, report, statement or demand required or permitted by any
provisions of this Agreement shall be in writing and shall be given by prepaid
telegraph, telecopy or certified mail addressed to the parties hereto at their
principal place of business.

10.  HEADINGS; COUNTERPARTS; GOVERNING LAW; ASSIGNMENT; LIMITATION OF LIABILITY

     10.1  The Article and paragraph headings contained in this Agreement are
for reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

     10.2  This Agreement may be executed in any number of counterparts each of
which shall be deemed an original.

     10.3  This Agreement shall be governed by and construed in accordance with
the laws of the Commonwealth of Massachusetts.

     10.4  This Agreement shall bind and inure to the benefit of the parties
hereto and their respective successors and assigns, but no assignment or
transfer hereof or of any rights or obligations hereunder shall be made by any
party without the written consent of the other party. Nothing herein expressed
or implied is intended or shall be construed to confer upon or give any person,
firm or corporation, other than the parties hereto and their respective
successors and assigns, any rights or remedies under or by reason of this
Agreement.

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     10.5  It is expressly agreed that the obligations of the Trust hereunder
shall not be binding upon any of the Trustees, shareholders, nominees, officers,
agents or employees of the Trust personally, but shall bind only the trust
property of the Trust, as provided in the Declaration of Trust of the Trust. The
execution and delivery by such officers of the Trust shall not be deemed to have
been made by any of them individually or to impose any liability on any of them
personally, but shall bind only the trust property of the Trust as provided in
the Declaration of Trust of the Trust. The Trust is a series company with
multiple series and has entered into this Agreement on behalf of the Predecessor
Fund and the Successor Fund.

     10.6  The sole remedy of a party hereto for a breach of any representation
or warranty made in this Agreement by the other party shall be an election by
the non-breaching party not to complete the transactions contemplated herein.

IN WITNESS WHEREOF, the undersigned has caused this Agreement to be executed as
of the date set forth above.

<Table>
                             
ATTEST                             JANUS INVESTMENT FUND
                                   For and on behalf of Janus Olympus Fund

Name:                              By:
       -------------------------      ------------------------------------
                                      Name:
                                      Title:

ATTEST                             JANUS INVESTMENT FUND
                                   For and on behalf of Janus Orion Fund

Name:                              By:
       -------------------------      ------------------------------------
                                      Name:
                                      Title:

ATTEST                             JANUS CAPITAL MANAGEMENT LLC

Name:                              By:
       -------------------------      ------------------------------------
                                      Name:
                                      Title:
</Table>

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