Ingres Database (/ɪŋˈɡrɛs/ ing-GRESS) is a proprietary SQL relational database management system intended to support large commercial and government applications.

Actian Corporation controls the development of Ingres and makes certified binaries available for download, as well as providing worldwide support. There was an open source release of Ingres but it is no longer available for download from Actian. However, there is a version of the source code still available on GitHub.

In its early years, Ingres was an important milestone in the history of database development. Ingres began as a research project at UC Berkeley, starting in the early 1970s and ending in 1985. During this time Ingres remained largely similar to IBM's seminal System R in concept; it differed in more permissive licensing of source code, in being based largely on DEC machines, both under UNIX and VAX/VMS, and in providing QUEL as a query language instead of SQL. QUEL was considered at the time to run truer to Edgar F. Codd's relational algebra (especially concerning composability), but SQL was easier to parse and less intimidating for those without a formal background in mathematics.

When ANSI preferred SQL over QUEL as part of the 1986 SQL standard (SQL-86), Ingres became less competitive against rival products such as Oracle until future Ingres versions also provided SQL. Many companies spun off of the original Ingres technology, including Actian itself, originally known as Relational Technology Inc., and the NonStop SQL database originally developed by Tandem Computers but now offered by Hewlett Packard Enterprise.

Ingres began as a research project at the University of California, Berkeley, starting in the early 1970s and ending in 1985. The original code, like that from other projects at Berkeley, was available at minimal cost under a version of the BSD license. Ingres spawned a number of commercial database applications, including Sybase, Microsoft SQL Server, NonStop SQL and a number of others.

Postgres (Post Ingres), a project which started in the mid-1980s, later evolved into PostgreSQL. It is ACID compatible and is fully transactional (including all DDL statements) and is part of the Lisog open-source stack initiative.

In 1973 when the System R project led by Edgar Codd was getting started at IBM, the research team released a series of papers describing the system they were building. Two scientists at Berkeley, Michael Stonebraker and Eugene Wong, became interested in the concept after reading the papers, and started a relational database research project of their own.

They had already raised money for researching a geographic database system for Berkeley's economics group, which they called Ingres, for INteractive Graphics REtrieval System. They decided to use this money to fund their relational project instead, and used this as a seed for a new and much larger project. They decided to re-use the original project name, and the new project became University INGRES. For further funding, Stonebraker approached the DARPA, the obvious funding source for computing research and development at the time, but both the DARPA and the Office of Naval Research (ONR) turned them down as they were already funding database research elsewhere. Stonebraker then introduced his idea to other agencies, and, with help from his colleagues he eventually obtained modest support from the NSF and three military agencies: the Air Force Office of Scientific Research, the Army Research Office, and the Naval Electronic Systems Command.