DB2 is IBM's Relational Database Management System software also known as data server. DB2 exists within IBM's broader Information Management Software line. Although there are different editions and versions of DB2 which run on devices ranging from handhelds to mainframes, most often DB2 refers to DB2 Enterprise Server Edition or the top-of-the-line DB2 Data Warehouse Edition (DB2 DWE), which runs on UNIX, Windows or Linux servers; or DB2 for z/OS.

For some years DB2, as a full-function DBMS, was exclusively available on IBM mainframes. Later DB2 introduced to other platforms, including OS/2, UNIX and Windows servers, then Linux (including Linux on zSeries) and PDAs. The inspiration for the mainframe version of DB2's architecture came in part from IBM DL/1 and IBM IMS, both initially hierarchical and then later network (or CODASYL) databases.

An earlier version of the code that would become DB2 LUW (Linux, Unix, Windows) was part of an Extended Edition component of OS/2 called Database Manager. IBM extended the functionality of Database Manager a number of times, including the addition of distributed database functionality that allowed shared access to a database in a remote location on a LAN. Eventually IBM declared that insurmountable complexity existed in the Database Manager code, and took the difficult decision to completely rewrite the software in their Toronto Lab. The new version of Database Manager, called DB2 like its mainframe parent, ran on the OS/2 and RS/6000 platforms, was called DB2/2 and DB2/6000 respectively. Other versions of DB2, with different code bases, followed the same '/' naming convention and became DB2/400 (for the AS/400), DB2/VSE (for the DOS/VSE environment) and DB2/VM (for the VM operating system). . At this point, the mainframe version of DB2 and the server version of DB2 are coded in entirely different languages (PL/S for the mainframe and C++ for the server), but shared very similar functionality and used a common architecture for SQL optimization: the Starburst Optimizer.

In the mid-1990s, IBM released a clustered DB2 implementation called DB2 Parallel Edition, which initially ran on AIX. This edition allowed scalability by providing a shared nothing architecture, in which a single large database is partitioned across multiple DB2 servers that communicate over a high-speed interconnect. This DB2 edition was eventually ported to all Linux, UNIX, and Windows (LUW) platforms and was renamed to DB2 Extended Enterprise Edition (EEE). IBM now refers to this product as the Database Partitioning Feature (DPF) and sells it as an add-on to their flagship DB2 Enterprise product.

In mid 2006, IBM announced "Viper," the codename for DB2 9 on distributed platforms and for DB2 9 on z/OS. IBM claims that the new DB2 will be the first relational database to store XML "natively". Other enhancements include OLTP-related improvements for distributed platforms, business intelligence/data warehousing-related improvements for z/OS, more self-tuning and self-managing features, additional 64-bit exploitation (especially for z/OS), stored procedure performance enhancements for z/OS, and continued convergence of the SQL vocabularies between z/OS and distributed platforms

On January 30th, 2006, IBM released a no-charge version of DB2 called DB2 Express-C. This was an expected response to the recently announced free versions of Oracle 10g and Microsoft SQL Server. Unlike Microsoft or Oracle's free editions, Express-C has no limit on number of users or on database size. While versions 8.2 and 9.1 of DB2 Express-C imposed hardware limits on the server on which it ran, DB2 Express-C 9.5 can run on Windows and Linux machines of any size, but the database engine will not utilize more than two CPU cores and 2GB RAM. In 2007, IBM introduced a yearly support subscription called the Fixed Term License (FTL), which offers a year of telephone support for Express-C for US$3000 per server. Purchasing the FTL also allows the DB2 Express-C engine to use up to four CPU cores and 4GB RAM. Users of DB2 Express-C who don't purchase an FTL subscription can receive support and assistance on a free, public web forum staffed by IBM technicians and other DB2 users.

CCG provides DB2 UDB consulting services for various products including,

• DB2 Universal Database v8.1 / v8.2 Editions

• Enterprise Server Edition (ESE)
• Workgroup Server Edition (WSE)
• Express Edition (EE)
• Personal Edition (PE)

• DB2 Universal Database v7.1 / v7.2 Editions

• Extended Enterprise Edition (EEE)
• Enterprise Edition (EE)
• Workgroup Edition (WE)
• Personal Edition (PE)

• DB2 Universal Database v6.1 Editions

• Extended Enterprise Edition (EEE)
• Enterprise Edition (EE)
• Workgroup Edition (WE)
• Personal Edition (PE)