Exhibit 31.1



CERTIFICATION PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY
ACT OF 2002

I, J. Michael Lawrie, certify that:

1.	I have reviewed this annual report on Form 10-K of
Siebel Systems, Inc.;

2. 	Based on my knowledge, this report does not contain
any untrue statement of a material fact or omit to state a material fact
necessary to make the statements made, in light of the circumstances under which
such statements were made, not misleading with respect to the period covered by
this report;

3. 	Based on my knowledge, the financial statements, and
other financial information included in this report, fairly present in all
material respects the financial condition, results of operations and cash flows
of the registrant as of, and for, the periods presented in this report;

4. 	The registrant's other certifying officer(s) and I are
responsible for establishing and maintaining disclosure controls and procedures
(as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control
over financial reporting (as defined in Exchange Act Rules 13a-15(f) and
15d-15(f)) for the registrant and have:

1. Designed such disclosure controls and procedures, or
caused such disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the registrant,
including its consolidated subsidiaries, is made known to us by others within
those entities, particularly during the period in which this report is being
prepared;
2. Designed such internal control over financial reporting,
or caused such internal control over financial reporting to be designed under
our supervision, to provide reasonable assurance regarding the reliability of
financial reporting and the preparation of financial statements for external
purposes in accordance with generally accepted accounting principles;
3. Evaluated the effectiveness of the registrant's
disclosure controls and procedures and presented in this report our conclusions
about the effectiveness of the disclosure controls and procedures, as of the end
of the period covered by this report based on such evaluation; and
4. Disclosed in this report any change in the registrant's
internal control over financial reporting that occurred during the registrant's
most recent fiscal quarter (the registrant's fourth fiscal quarter in the case
of an annual report) that has materially affected, or is reasonably likely to
materially affect, the registrant's internal control over financial reporting;
and

5. 	The registrant's other certifying officer(s) and I
have disclosed, based on our most recent evaluation of internal control over
financial reporting, to the registrant's auditors and the audit committee of the
registrant's board of directors (or persons performing the equivalent
functions):

1. All significant deficiencies and material weaknesses in
the design or operation of internal control over financial reporting which are
reasonably likely to adversely affect the registrant's ability to record,
process, summarize and report financial information; and
2. Any fraud, whether or not material, that involves
management or other employees who have a significant role in the registrant's
internal control over financial reporting.

Dated: March 9, 2005

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| | By: | /s/ J. Michael Lawrie
                                      J. Michael Lawrie
                                Chief Executive Officer

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