Formentera is the smallest and more southerly island of the Pityusic Islands group (comprising Ibiza and Formentera, as well as various small islets), which belongs to the Balearic Islands autonomous community (Spain). It covers an area of 83.22 square kilometres (32.13 sq mi) (including offshore islets) and had a population of 10,582 at the Census of 1 November 2011; the latest official estimate (as at 1 January 2019) was 12,111.

The main island of Formentera is 19 kilometres (12 mi) long and is located about 6 kilometres (4 mi) south of Ibiza in the Mediterranean Sea. More specifically Formentera is part of the delimitation of the Balearic Sea which is a northwestern element of the Mediterranean Sea. Its major villages are Sant Francesc Xavier, Sant Ferran de ses Roques, El Pilar de la Mola and La Savina.

Formentera comprises one municipality, also called Formentera, and has a population of 9,962 (as at 1 January 2010). Its land area is 83.24 square kilometres (32.1 sq mi). It is subdivided into several civil parishes (parròquies), themselves subdivided into vendas.

North of Formentera is the island of Espalmador (Illa de s'Empalmador in Catalan), which is the second largest island of the municipality, and is itself surrounded by a few minor islets. Espalmador is a tombolo, separated from the main island of Formentera by a shallow sandbar, and during low tide, it is possible for one to wade between the two islands. This area is a popular stopping point for those in yachts heading between Ibiza and Formentera.