THIS IS HYBRID is an updated and enlarged selection of the articles and projects published initially in the Hybrids series of the a+t magazine.

The prologue, written by Steven Holl specially for this compilation, puts forward the potential of hybrid buildings in the 21st Century.

Research on new prototypes, conducted by Iñaki Ábalos at AAP-Cornell GSD-Harvard and BIArch-Barcelona completes this volume in which reality is closer to utopia.

Our home is now in the city which is compacted and mixed up, which grows inwards and is renewed. We are returning to the historic city, to the modern city, to the post-industrial city, we are re-densifying the expansive city of the last decade. We are regenerating the narrow plots of the medieval urban grids, the 19th century urban extensions and the new-old cities of the 60s. We are returning to the built-up city driven by the need to save on resources, but this return cannot be a reluctant one.

DENSITY IS HOME echoes these types of city -dispersed, expansive, modern, the core of the city and the recycled city- through 37 projects on collective housing. 14 case studies have been extracted among them in order to analyze the desirable home.

The book forms part of the Density series, initiated by a+t in 2002, which became a reference for publications about collective housing worldwide.

The volume by a+t publishers is part of the Density series on collective housing.

Next focuses mainly on infills of the consolidated urban fabric. All projects have won first or second prizes in international competitions and fill in the existing city or regenerated urban voids with different former uses.

Next analyzes 30 European and American projects by 29 different young architectural practices.

The volume published by a+t forms part of the Density series, dedicated to the analysis of collective housing.

HoCo is noted for including construction systems within the field of study and comparison, besides the costs of each project:

• Comparative analysis of 32 collective housing projects.
• Build cost per square metre comparison.
• Sustainability strategies followed in each project.
• Comparison of density and its implementation in the context.
• 66 construction details analyzed, compared and arranged by facades and roofs.

The Public Chance is a visual analysis of 30 urban landscapes of opportunity. It is the first book published in the In Common series, which came about in 2005 in the pages of a+t magazine in order to express the publisher's concern for the good use and design of public space.

DBOOK consists of 64 collective housing projects, analyzed and compared regarding their contribution to the dense city.

After the publication of Density, New Collective Housing, DBOOK is the next step in the dissemination of examples that encourage the compact development of urban centers.

Density projects contains 36 ideas on collective housing that are committed to increasing density. They are projects that propose savings in land use and, consequently, a more sustainable environment.

The design strategy of the authors, the implementation in the context and the development of the housing typologies are analysed and compared by themes, following the path begun by the a+t series dedicated to Density. The projects, in phase of development or execution throughout 2007, are characterised for favouring densification through good architecture. Many of them include other uses besides residential uses in their programmes. This contributes not only density, but also intensity to their respective environments.

We believe that the combination of different functions inside the same project is the key to the regeneration of the consolidated city and for the creation of new urban nuclei and that collective housing in this context of mixed-use, generating a dense built environment, is the only solution to the consumption of resources.