Squatting (understood as the appropriation and use of land and/or built space without legal title) is not a new phenomenon in human history. There is no doubt, however, that the extent and visibility of squatting greatly increased since the 1950s.1 Throughout the second half of the twentieth century, different forms of squatting became the means through which a growing number of migrant families and newly formed households acquired their first homes in urban regions. Newly arrived migrants solved the problems of homelessness and of unemployment through a variety of self-help and often illegal initiatives.2 This chapter examines the phenomenon of squatting in Spain. Starting in 1955, it spans the second half of General Francisco Franco’s dictatorship (1939-1975) and the years of Spain’s transition to democracy (1975-1982). My aim is to analyse the conditions that facilitated large-scale migration from the countryside to Spain’s major cities and generated the construction of hundreds of shanty towns during the late 1950s. I will then focus on the case of three major shanty towns in Madrid and describe their formation and their struggle for legal recognition.