A condominium, or condo, is the form of housing tenure and other real property where a specified part of a piece of real estate (usually of an apartment house) is individually owned while use of and access to common facilities in the piece such as hallways, heating system, elevators, exterior areas is executed under legal rights associated with the individual ownership and controlled by the association of owners that jointly represent ownership of the whole piece. Colloquially, the term is often used to refer to the unit itself in place of the word "apartment". A condominium may be simply defined as an "apartment" that the tenant "owns" as opposed to rents.

The difference between a condominium and an apartment is purely legal: there is no way to know a condo from an apartment simply by looking at or visiting the building. What defines a condominium is the form of ownership. The same building developed as a condominium (and sold as individual units to different owners) could actually be built someplace else as an apartment building (the developers would retain onwnership and rent individual units to different tenants).

Condominium is the legal term used in the United States and in most provinces of Canada. In Australia and the Canadian province of British Columbia it is referred to as strata title. In Quebec the term "divided co-property" ( ) is used, although the colloquial name remains 'condominium'. In England and Wales the equivalent is commonhold, a form of ownership introduced in 2004 and still uncommon in most places. In France the equivalent is called Copropriété (co-ownership), usually managed by the Syndic.

Technically, a condominium is a collection of individual home units along with the land upon which they sit. Individual home ownership within a condominium is construed as ownership of only the air space confining the boundaries of the home (Anglo-Saxon law systems; different elsewhere). The boundaries of that space are specified by a legal document known as a Declaration, filed of record with the local governing authority. Typically these boundaries will include the drywall surrounding a room, allowing the homeowner to make some interior modifications without impacting the common area. Anything outside this boundary is held in an undivided ownership interest by a corporation established at the time of the condominium's creation. The corporation holds this property in trust on behalf of the homeowners as a group–-it may not have ownership itself.

The primary attraction to this type of ownership is the ability to obtain affordable housing in a highly desirable area that typically is beyond economic reach. Additionally, such properties benefit from having restrictions that maintain and enhance value, providing control over blight that plagues some neighborhoods. Major American cities, including Miami, San Francisco, Chicago, New York City, Los Angeles, and Washington D.C., have abundant condo development.