The move is significant as the industry establishes the standards that will underpin next-generation software.
Software developers from both companies will work together to integrate Siebel's CRM (customer relationship management) software with IBM's WebSphere application server and related products that are based on J2EE (Java 2 Enterprise Edition).
The pledge of support for J2EE comes three months after Siebel signed a broad joint development deal with Microsoft to make its products work with Microsoft's .net platform, which rivals the J2EE platform.
Siebel and IBM have been jointly selling Siebel's CRM products since 1999. The alliance has resulted in more than 1,000 joint customers, including Bank of America and Caterpillar. The J2EE announcement is an expansion of that alliance.