The architecture magazine a+t puts together in a book its four issues on Density and mass housing, revised and extended with new projects. The selection includes over 60 buildings and ten executed urban plans. The publication takes on the character of an accessible manual: the projects are presented in a uniform manner and the data offered can be easily compared. The monograph is structured according to Density (number of dwellings per hectare), always however taking into account the different ways of occupying land and the new factors bearing on the design of collective housing. The quality and quantity of the projects selected and the way they are presented over 300 photos including overall plans, floor plans of apartments, and working details make this manual a first major worldwide revision of mass housing, one tackled through a reflection on density. A detailed, meticulously elaborated work based on studies on housing carried out in the past five years on an international scale. Indexes organized by author, formal result, and manner of occupying land. An indispensable reference for the architect committed to his times and for anyone interested in the new tendencies of mass housing • 10 urban plans • 65 built projects • plans at scale 1:500 • details at scale 1:20 • comparative analysis considering layout and housing form