SAP ASE (Adaptive Server Enterprise), originally known as Sybase SQL Server, and also commonly known as Sybase DB or Sybase ASE, is a relational model database server developed by Sybase Corporation, which later became part of SAP SE. ASE was developed for the Unix operating system, and is also available for Microsoft Windows.

In 1988, Sybase, Microsoft and Ashton-Tate began development of a version of SQL Server for OS/2, but Ashton-Tate later left the group and Microsoft went on to port the system to Windows NT. When the agreement expired in 1993, Microsoft purchased a license for the source code and began to sell this product as Microsoft SQL Server. MS SQL Server and Sybase SQL Server share many features and syntax peculiarities.

Bob Epstein left Britton Lee, Inc. to help found Sybase and carried a lot of the ideas from the hardware database with him, reasoning that standard hardware such as Intel, Motorola and Sun 32 and 64 bit processors running database software could advance much more rapidly than specialist hardware. Originally developed for Unix operating system platforms in 1987, Sybase Corporation's primary relational database management system product was initially marketed under the name Sybase SQL Server. Microsoft's Bill Gates praised it as the world's best SQL database engine; in 1988, SQL Server for OS/2 was co-developed for the PC by Sybase, Microsoft, and Ashton-Tate. Ashton-Tate divested its interest and Microsoft became the lead partner after porting SQL Server to Windows NT. Microsoft and Sybase sold and supported the product through version 4.2.1.

The key feature that made SQL Server attractive from the start was its high performance due to shared log writes, clustered indexes and a small memory footprint per user. As a result of these and other design features it performed well "out of the box".

Sybase released SQL Server 4.2 in 1992. This release included internationalization and localization and support for symmetric multiprocessing systems.

In 1993, the co-development licensing agreement between Microsoft and Sybase ended, and the companies parted ways after an amicable solution was reached. Sybase wanted to develop on the Intel Unix platform and Microsoft wanted Windows specific solutions. As part of the agreement Sybase released the System 10 codeline to Microsoft and Microsoft gave up exclusive rights to Intel platforms. Both continuing to independently develop their respective versions of SQL Server. Sybase released Sybase SQL Server 10.0, which was part of the System 10 product family, which also included Back-up Server ( a very high performance parallel backup process), Replication Server ( to provide replicate sites), Navigation Server ( a shared nothing parallel server), Open Client/Server APIs, SQL Monitor, SA Companion and OmniSQL Gateway. Microsoft continued on with Microsoft SQL Server.

Sybase provides native low-level programming interfaces to its database server which uses a protocol called Tabular Data Stream. Prior to version 10, DBLIB (DataBase LIBrary) was used. Version 10 and onwards uses CTLIB (ClienT LIBrary).

In 1995, Sybase released SQL Server 11.0. Starting with version 11.5 released in 1996, Sybase moved to differentiate its product from Microsoft SQL Server by renaming it to Adaptive Server Enterprise. Sybase 11.5 added Asynchronous prefetch, case expression in sql, the optimizer can use a descending index to avoid the need for a worktable and a sort. The Logical Process Manager was added to allow prioritization by assigning execution attributes and engine affinity.