When is a house ecological? Does the use of natural materials and solar cells on the roof make a building an example of ''green'' architecture? Perhaps even Antoni Gaudí and Frank Lloyd Wright designed ''greener'' buildings than most contemporary architects, whose low-energy houses scarcely differ outwardly from traditional ones. James Wines puts up the various - and often irreconcilable - concepts of environmentally-friendly architecture for discussion, making a case for an architecture that not only focuses on technological solutions, but also tries to reconcile man and nature in its formal idiom. Among the examples of contemporary ecological architecture presented are works by Emilio Ambasz, Gustav Peichl, and others.