A gazetteer is a geographical dictionary or directory used in conjunction with a map or atlas. It typically contains information concerning the geographical makeup, social statistics and physical features of a country, region, or continent. Content of a gazetteer can include a subject's location, dimensions of peaks and waterways, population, gross domestic product and literacy rate. This information is generally divided into topics with entries listed in alphabetical order.

Ancient Greek gazetteers are known to have existed since the Hellenistic era. The first known Chinese gazetteer was released by the first century, and with the age of print media in China by the ninth century, the Chinese gentry became invested in producing gazetteers for their local areas as a source of information as well as local pride. The geographer Stephanus of Byzantium wrote a geographical dictionary (which currently has missing parts) in the sixth century which influenced later European compilers. Modern gazetteers can be found in reference sections of most libraries as well as on the internet.

The Oxford English Dictionary defines a "gazetteer" as a "geographical index or dictionary". It includes as an example a work by the British historian Laurence Echard (d. 1730) in 1693 that bore the title "The Gazetteer's: or Newsman's Interpreter: Being a Geographical Index". Echard wrote that the title "Gazetteer's" was suggested to him by a "very eminent person" whose name he chose not to disclose. For Part II of this work published in 1704, Echard referred to the book simply as "the Gazeteer". This marked the introduction of the word "gazetteer" into the English language. Historian Robert C. White suggests that the "very eminent person" written of by Echard was his colleague Edmund Bohun, and chose not to mention Bohun because he became associated with the Jacobite movement.

Since the 18th century, the word "gazetteer" has been used interchangeably to define either its traditional meaning (i.e., a geographical dictionary or directory) or a daily newspaper, such as the London Gazetteer.

Gazetteers are often categorized by the type, and scope, of the information presented. World gazetteers usually consist of an alphabetical listing of countries, with pertinent statistics for each one, with some gazetteers listing information on individual cities, towns, villages, and other settlements of varying sizes. Short-form gazetteers, often used in conjunction with computer mapping and GIS systems, may simply contain a list of place-names together with their locations in latitude and longitude or other spatial referencing systems (e.g., British National Grid reference). Short-form gazetteers appear as a place–name index in the rear of major published atlases. Descriptive gazetteers may include lengthy textual descriptions of the places they contain, including explanation of industries, government, geography, together with historical perspectives, maps and/or photographs. Thematic gazetteers list places or geographical features by theme; for example fishing ports, nuclear power stations, or historic buildings. Their common element is that the geographical location is an important attribute of the features listed.

Gazetteer editors gather facts and other information from official government reports, the census, chambers of commerce, together with numerous other sources, and organise these in digest form.

In his journal article "Alexander and the Ganges" (1923), the 20th-century historian W.W. Tarn calls a list and description of satrapies of Alexander's Empire written between 324 and 323 BC as an ancient gazetteer. Tarn notes that the document is dated no later than June 323 BC, since it features Babylon as not yet partitioned by Alexander's generals. It was revised by the Greek historian Diodorus Siculus in the 1st century BC. In the 1st century BC, Dionysius of Halicarnassus mentioned the chronicle-type format of the writing of the logographers in the age before the founder of the Greek historiographic tradition, Herodotus (i.e., before the 480s BC), saying "they did not write connected accounts but instead broke them up according to peoples and cities, treating each separately". Historian Truesdell S. Brown asserts that what Dionysius describes in this quote about the logographers should be categorized not as a true "history" but rather as a gazetteer. While discussing the Greek conception of the river delta in ancient Greek literature, Francis Celoria notes that both Ptolemy and Pausanias of the 2nd century AD provided gazetteer information on geographical terms.

Perhaps predating Greek gazetteers were those made in ancient Egypt. Although she does not specifically label the document as a gazetteer, Penelope Wilson (Department of Archaeology, Durham University) describes an ancient Egyptian papyrus found at the site of Tanis, Egypt (a city founded during the Twentieth dynasty of Egypt), which provides the following for each administrative area of Egypt at the time: