This book is the result of contributions, help and support from numerous people and several agencies. We are particularly grateful to the Swedish Agency for Research Cooperation with Developing Countries, the Swedish Council for Building Research and the United Nations Centre for Human Settlements (Habitat) for funding the work on which this volume is based - and doing so before the subject had come to be regarded as important and relevant. Within these agencies, special thanks is due to Olle Edqvist, Pietro Garau, Bruce Hyland, Bob and Ingrid Munro and Arcot Ramachandran. We are also grateful to our friends and colleagues in IIED's Human Settlements Programme who have worked with us on this subject - Jane Bicknell, Silvia Blitzer, Ana Maria Cabrera, Maria Graciela Caputo and Julio Davila. Julio Davila deserves special thanks for his help in refining and editing the final text; so too do Jane Bicknell and Ana Maria Cabrera for patiently putting up with endless last minute changes to the text.