The city of Castelo Branco is a municipality and former bishopric in Castelo Branco District, in Centro Region, Portugal. The name means "white castle" in Portuguese.

The city of Castelo Branco is made up of 19 Freguesias (civil parish) with a population of 30,649 in 2001. The municipality has a total of 19 parishes. The population in 2011 was 56,109, in an area of 1,438.19 square kilometres (555.29 square miles), making it one of the largest municipalities in Portugal.

It is bounded in the north by the municipality of Fundão, in the east by Idanha-a-Nova, in the south by Spain, in the southwest by Vila Velha de Ródão, and in the west by Proença-a-Nova and Oleiros.

The most important monument in Castelo Branco is the Jardim do Paço Episcopal (Garden of the Episcopal Palace). It is one of the most beautiful baroque gardens in Portugal and contains statues of allegories, kings and zodiacal signs, arranged around ponds, terraces and staircases.