---

---

Exhibit 12.1

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

I, Boaz Raviv, certify
that:

|1. | I
have reviewed this annual report on Form 20-F of RADVISION Ltd.;
|-- | ------------------------------------------------------------------

|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 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:
|-- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (a) | 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;
| | --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (b) | 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;
| | --- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (c) | 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
| | --- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (d) | Disclosed
in this report any change in the Registrants internal control                over
financial reporting that occurred during the period covered by the 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 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 function):
|-- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (a) | 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
| | --- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (b) | 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.
| | --- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Date: June 4, 2007

|/s/ Boaz Raviv*
Boaz RavivChief Executive Officer |  | 
|--------------------------------------------------------------- |  | 

*     The
originally executed copy of this Certification will be maintained at the Registrants
offices and will be made available for inspection upon request.



---

---