Geo is a microformat used for marking up geographical coordinates (latitude and longitude) in HTML (or XHTML). Coordinates are expected in angular units of degrees and geodetic datum WGS84. Although termed a "draft" specification, the format is a de facto standard, stable and in widespread use; not least as a sub-set of the published hCalendar and hCard microformat specifications, neither of which is still a draft.

Use of Geo allows parsing tools (for example other websites, or Firefox's Operator extension) to extract the locations, and display them using some other website or web mapping tool, or to load them into a GPS device, index or aggregate them, or convert them into an alternative format.

The Geo microformat is applied using three HTML classes. For example, the marked-up text:

becomes:

by adding the class-attribute values "geo", "latitude" and "longitude".

This will display

Belvide: 52.686; -2.193

and a geo microformat for that location, Belvide Reservoir, which will be detected, on this page, by microformat parsing tools.