Castellar de la Frontera is a town and municipality located in the province of Cádiz, in Andalusia, Spain.

Castellar de la Frontera is a village within a castle surrounded by the walls of a well preserved Moorish-Christian fortress.

It is located within the Parque Natural de Los Alcornocales next to a reservoir formed by the Guadarranque River.

The derelict state of the village attracted a number of Germans who took over the empty houses and built temporary dwellings outside the walls.

Castellar is in an isolated location, at the end of a mountain road that runs off the A-368.