The collegiate options considered by more than one-half million high school seniors in the eastern third of the nation are analyzed, and perspectives are offered on enrollment planning. A framework for public and institutional policies is provided, along with a vocabulary to describe the actual workings of the higher education market. The origins and current applications of the Market Segment Model are also described. Attention is directed to how students in each segment differ and what makes high school seniors choose institutions close/far away. From the institutional point of view, consideration is given to colleges' competition for local/national students and a possible structure to competitive relationships. Policy dimensions addressed concern the way that demographics and the economy combine to establish the college participation rate. Finally, public policy initiatives are suggested that may ameliorate the negative aspects of institutional competition. Appended data cover the following: socioeconomic attributes in the Middle States and the South; New England, Middle States, and Southern markets; a discussion of the stability of market segment distribution; information on score submission and matriculation for the Scholastic Aptitude Test. (Author/SW)