PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS "spatially enables" the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS), much like ESRI's SDE or Oracle's Spatial extension. PostGIS follows the OpenGIS "Simple Features Specification for SQL" and has been certified as compliant with the "Types and Functions" profile.

PostGIS development was started by Refractions Research as a project in open source spatial database technology. PostGIS is released under the GNU General Public License. PostGIS continues to be developed by a group of contributors led by a Project Steering Committee and new features continue to be added.