Files with the .GML extension contain geographical data saved in a format based on XML structure and allow for a graphical presentation of various types of data, such as vectors, points, and areas. The files are used for saving such data in geographical information system applications and for standardized exchanges between such applications.

The format was created by Galdos Systems and is supported by the Open Geospatial Consortium; the standard is officially defined in the ISO 19136:2007 norm. The data structure in GML files can be defined using a XSD schema file.