Planning for regional development forms the major theme of this study. The purpose of the study is to demonstrate the hypothesis, that the effectiveness of regional planning as a tool of development is dependent upon the ability to make power, function and region or area coincide. The approach taken in the study was, first, to discuss the problem in a general way. Growing urbanization and its manifested ills is used to illustrate the need for regional development in the less developed sector of the world's economy. The growth of the regional concept in the major disciplines related to planning is traced, and the application of this concept in the United States and the newly independent countries is examined. Attention is drawn to the state of planning for regional development and the need for a closer relationship between power, function and region. In order to test the hypothesis a case study of Puerto Rico is undertaken. The choice of the territory was prompted by two factors. In the first instance, Puerto Rico is claimed to be a model of development in the Western Hemisphere. Secondly, as Puerto Rico is an island it is a clearly delineated region. The method employed was to try to evaluate the developmental achievement of Puerto Rico and at the same time assess the factors involved. The procedure was as follows. Noting that 1940 marked the beginning of the developmental programme, and 1898 the end of Spanish rule on the island, the intervening period was assessed from an economic and social point of view. Starting from 1940 the main features contributing to development from a planning standpoint were considered. Prior to embarking on a discussion of the developmental achievements, the factors unique to the island that would have contributed to development are outlined. The case study concludes with specific indices of development. The conclusions drawn from the analysis are: That the development process in Puerto Rico is a success, and that this success resulted from a series of incidents which seemed to occur fortuitously. These were: The coming to power of the Popular Democratic Party led by Munoz Marin; the appointment of Rexford G. Tugwell as Governor; and the constitutional changes which took place when Puerto Rico gained Commonwealth Status. Munoz Marin was a leader dedicated to the development of the Island and Rexford Tugwell was a planner seeking to create a planning administration with jurisdiction over the area or region in which the functions to be planned existed; and endowed with the power to implement the plans designed. Although Tugwell was not totally successful in creating his ideal administrative framework, he was able to bring power, function and region into a close relationship. The study also brought to light certain subsidiary criteria that are essential for the triad - power, function and region - to work effectively for regional development. These are: Size of population, services rendered, legal authorization, fiscal adequacy, accountability and flexibility. These, together with power, region and function form the components of a suggested model useful in assessing the effectiveness of organization for regional development. / Applied Science, Faculty of / Community and Regional Planning (SCARP), School of / Graduate