The OpenDocument Format (ODF) is an open XML-based document file format for office applications to be used for documents containing text, spreadsheets, charts, and graphical elements. The file format makes transformations to other formats simple by leveraging and reusing existing standards wherever possible.

ODF is defined via an open and transparent process at OASIS (Organization for the Advancement of Structured Information Standards) and has been approved unanimously by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) as an international standard in May 2006. It is available for implementation and use free of any licensing, royalty payments, or other restrictions.

From a technical point of view, ODF is a ZIP archive that contains a collection of different XML files as well as binary files like embedded images. The use of XML makes accessing the document content simple because content can be opened and changed with simple text editors if necessary. In contrast, the previously used binary file formats were cryptic and difficult to process. The ZIP compression guarantees relatively small file sizes, in order to reduce file storage and transmission bandwidth requirements. ODF was the first broadly used document file format that used the concept of a ZIP package containing different XML files. ODF uses the same set of XML files for different application types. In addition, definitions for elements like tables are consistent across application types as well.

The OpenDocument format has a long tradition of openness. The first work on the file format started as early as 1999. Right from the beginning ODF was designed as an open and implementation neutral file format.

The open specification process started in 2000 with the foundation of the OpenOffice.org open source project and the community efforts within its XML development project. An even higher level of openness was established in 2002 with the creation of the OASIS Open Office Technical Committee (TC).

During the last seven years an increasing number of organizations and companies joined the ODF specification process. In addition, a growing number of applications implements the OpenDocument file format.

The OpenDocument Format was designed to be vendor neutral and implementation agnostic. In order to simplify transformations and to maximiz interoperability, the format reuses established standards like HTML, SVG, XSL, SMIL, XLink, XForms, MathML, and Dublin Core. ODF files of different application types (e.g. word processor, spredsheet) include the same set of XML files within the ZIP packages.