A merger, consolidation or amalgamation, in a political or administrative sense, is the combination of two or more political or administrative entities, such as municipalities (in other words cities, towns, etc.), counties, districts, etc., into a single entity. This term is used when the process occurs within a sovereign entity.

Unbalanced growth or outward expansion of one neighbor may necessitate an administrative decision to merge (see urban sprawl). In some cases, common perception of continuity may be a factor in prompting such a process (see conurbation). Some cities (see below) that have gone through amalgamation or a similar process had several administrative sub-divisions or jurisdictions, each with a separate person in charge.

Annexation is similar to amalgamation, but differs in being applied mainly to two cases:

The units joined are sovereign entities before the process, as opposed to being units of a single political entity.

A city's boundaries are expanded by adding territories not already incorporated as cities or villages.