Martínez provides a general introduction to the book by presenting the aims of the collective research which was undertaken by the contributors. This chapter constructs a theoretical framework with the main concepts that served as a guideline for the writing of individual chapters. In particular, Martínez focuses on the notions of ‘protest cycle’ and ‘socio-spatial structures’ and applies them to the study of squatters’ movements. The distinction between squatting practices and movements is also introduced. A final section notes the comparative approach based on specific databases for each city.