These are the Proceedings of the PLEA'91 meeting, held in Seville under the joint responsability of the International Steering Committee of PLEA -Passive and Low Energy Architecture -and of a local organizing committee hosted by several research groups of the University of Seville. This is the ninth annual PLEA Conference organized since 1982 in response to the per manent commitment of PLEA; to become close to the regional problems to contribute for the widening and the enhancement of the understanding of the problems associated with the built environment. to its general principles and objectives, PLEA aims to establish the highest According standard of research but, also, to promote professionalism in building science and construc tion technology and in architecture and urbanism. While recognizing that the adoption of an "environment-conscious design" will help significantly towards solving some of our current environmental problems, PLEA advocates that the environment-conscious design is not just a means for avoiding ecological disaster, but a criterion of architectural quality and a creative meeting point between science, technology and architecture.