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OpenStreetMap (OSM) is a map database maintained by a community of volunteers via open collaboration. Contributors collect data from surveys, trace from aerial photo imagery or satellite imagery, and import from other freely licensed geodata sources.

OpenStreetMap is freely licensed under the Open Database License and is commonly used to make electronic maps, inform turn-by-turn navigation, and assist in humanitarian aid and data visualisation. OpenStreetMap uses its own data model to store geographical features which can then be exported into other GIS file formats. The OpenStreetMap website itself is an online map, geodata search engine, and editor.

OpenStreetMap was created by Steve Coast in response to the Ordnance Survey, the United Kingdom's national mapping agency, failing to release its data to the public under free licences in 2004. Initially, maps in OSM were created only via GPS traces, but it was quickly populated by importing public domain geographical data such as the U.S. TIGER and by tracing imagery as permitted by source. OpenStreetMap's adoption was accelerated by the development of supporting software and applications and Google Maps' 2012 introduction of pricing.

The database is hosted by the OpenStreetMap Foundation, a non-profit organisation registered in England and Wales, and is funded mostly via donations.

Steve Coast founded the project in 2004 while attending University College London, initially focusing on mapping the United Kingdom. In the UK and elsewhere, government-run and tax-funded projects like the Ordnance Survey created massive datasets but declined to freely and widely distribute them. The first contribution was a street that Coast entered in December 2004 after cycling around Regent's Park in London with a GPS tracking unit. In April 2006, the OpenStreetMap Foundation was established to encourage the growth, development and distribution of free geospatial data and provide geospatial data for anybody to use and share.

In April 2007, Automotive Navigation Data (AND) donated a complete road data set for the Netherlands and trunk road data for India and China to the project. By July 2007, when the first "State of the Map" (SotM) conference was held, there were 9,000 registered users. In October 2007, OpenStreetMap completed the import of a US Census TIGER road dataset. In December 2007, Oxford University became the first major organisation to use OpenStreetMap data on their main website. Ways to import and export data have continued to grow – by 2008, the project developed tools to export OpenStreetMap data to power portable GPS units, replacing their existing proprietary and out-of-date maps. In March 2008, two founders of CloudMade, a commercial company that uses OpenStreetMap data, announced that they had received venture capital funding of €2.4 million. In 2010, AOL launched an OSM-based version of MapQuest and committed $1 million to increasing OSM's coverage of local communities for its Patch website.

The OSM project aims to collect data about stationary objects throughout the world, including infrastructure and other aspects of the built environment, points of interest, land use and cover classifications, and topography. Map features range in scale from international boundaries to hyperlocal details such as shops and street furniture. Although historically significant features and ongoing construction projects are routinely included in the database, the project's scope is limited to the present day, as opposed to the past or future.

OSM's data model differs markedly from that of a conventional GIS or CAD system. It is a topological data structure without the formal concept of a layer, allowing thematically diverse data to commingle and interconnect. A map feature or element is modelled as one of three geometric primitives:

A node is a point with a geographic coordinate expressed in the WGS 84 coordinate system. A standalone node represents a point of interest, such as a mountain peak.

A way is an ordered list of nodes that represents a polyline or polygon, depending on its metadata and whether it forms a closed ring. A way can represent either a linear feature, such as a street or river, or an area, such as a forest, park, parking lot, or lake. Multiple ways can share a node to represent a connection, for instance, a street intersection or a confluence of two rivers. The node itself can simultaneously represent another feature, for example, an entrance that connects a footway to a building. Until 2007, a way was formally composed of explicit segments between pairs of nodes.