The present monograph is a synthesis of what has been contributed during the last decade to the analysis of market demand in large econ­ omies where consumers may have non-convex preference relations. Al­ though research in this field has not yet come to an end there exists a variety of interesting results, established in different frameworks by means of different conceptual and formal tools. a It is my aim to give comprehensive treatment of the existing lit­ erature including my own contributions. In working out differences and interrelations of the various ap­ proaches I adopted and modified several of the original results. My desire to present