Each municipality is led by a mayor and divided into barrios, third-level administrative divisions, though the latter are not vested with any political authority.

Each legislature must be unicameral, with the number of members related to adequate representation of the total population of the municipality.

In contrast to other jurisdictions, both the mayors and the municipal legislators are elected on the same date and for the same term of four years in office.

[2] Statistically, the municipality with the largest number of inhabitants is San Juan, with 342,259, while Culebra is the smallest, with around 1,792.

[3] All municipalities have a barrio called pueblo proper, officially called barrio-pueblo (literally "district-town"), which typically is the site of the historic Spanish colonial settlement, administrative center and urban core of the municipality.

In Recent Civic Architecture in Porto Rico by Adrian C. Finlayson, architect for the Insular Department of the Interior Architecture, writing for the publication Architectural Record in 1920, the Puerto Rican municipality is accurately described as: Not merely a city, but something similar to a wide-extending township in New England—like Plymouth, Massachusetts, or Barnstable, on Cape Cod comprising a central town or city with perhaps several outlying districts or barrios, usually rural in character, and occasionally having sizeable concentrated populations in villages, the municipality bearing the name of the central urban portion and all under one local government.

Thus, there are no literal first-order administrative divisions akin to counties, as defined by the U.S. Federal Government.

[30][31] In March 2019, then Governor Ricardo Rosselló created an initiative that would preserve the existing municipalities but create regional consolidation by sharing service overhead in the form of counties but he resigned prior to anything coming of his proposal.