Room 4561
				July 14, 2005



Matthew Hale
Chief Financial Officer
S1 Corporation
3500 Lenox Road, NE
Suite 200
Atlanta, GA 30326

Re:	S1 Corporation
	Form 10-K for Fiscal Fear Ended December 31, 2004
	Filed March 16, 2005
		File No. 000-24931


Dear Mr. Hale:

      We have reviewed your response letter dated June 20, 2005
and
have the following additional comments.  Where indicated, we think
you should revise your document in response to these comments.  If
you disagree, we will consider your explanation as to why our
comment
is inapplicable or a revision is unnecessary.  Please be as
detailed
as necessary in your explanation.  In some of our comments, we may
ask you to provide us with supplemental information so we may
better
understand your disclosure.  After reviewing this information, we
may
raise additional comments.

	Please understand that the purpose of our review process is
to
assist you in your compliance with the applicable disclosure
requirements and to enhance the overall disclosure in your filing.
We look forward to working with you in these respects.  We welcome
any questions you may have about our comments or any other aspect
of
our review.  Feel free to call us at the telephone numbers listed
at
the end of this letter.


Form 10-K for the year ended December 31, 2004
Item 8.  Financial Statements and Supplementary Data, page 41

Consolidated Statements of Operations, page 45

1. We note your response to prior comment number 4.  We note that
your statement of operations does not include a gross margin line
item; however, both MD&A and your quarterly financial data
disclose
and discuss "gross margin." Revise the statement of operations,
MD&A
and the quarterly financial data to include the amortization of
purchased technology and software development costs as a component
of
"cost of revenues." We reference Question 17 of the SFAS 86 FASB
Implementation Guide. Your MD&A and quarterly presentation of
operating results should be revised as well. We note that SAB
Topic
11:B addresses the accounting for depreciation.

Note 2. Summary of Significant Accounting Policies, page 48

Financial instruments, page 49

2. We note your response to prior comment number 5.  Revise the
disclosures in the "Reclassification" policy of your Form 10-K to
quantify the effect the reclassification had on your balance sheet
and statement of cash flows. Your revisions should also refer to
the
fact that the reclass was made in order to comply with SFAS 95.

	As appropriate, please amend your filing and respond to these
comments within 10 business days or tell us when you will provide
us
with a response.  Please submit all correspondence and
supplemental
materials on EDGAR as required by Rule 101 of Regulation S-T.  You
may wish to provide us with marked copies of any amendment to
expedite our review.  Please furnish a cover letter with any
amendment that keys your responses to our comments and provides
any
requested information.  Detailed cover letters greatly facilitate
our
review.  Please understand that we may have additional comments
after
reviewing any amendment and your responses to our comments.

	You may contact Christine Davis, Staff Accountant, at (202)
551-
3408, Marc Thomas, Review Accountant at (202) 551-3452 or me at
(202)
551-3489 if you have questions regarding these comments.

Sincerely,


      Brad Skinner
							Accounting Branch Chief
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Mr. Matthew Hale
S1 Corporation
July 14, 2005
Page 2