This paper provides an overview of the controversy concerning "freedom of choice" desegregation plans and presents a case study of the plan adopted by Cambridge, Massachusetts, in 1981. Following the introduction, a short explanation of the plan's distinctive feature, controlled open enrollment, is given. (Under controlled open enrollment, no students are assigned to schools on the basis of their home residence. Instead, parents must choose the schools they want their children to attend before they are enrolled in the system, all student assigments are subject to explicit desegregation controls, and no students are given absolute guarantees of attending one particular school.) Next, enrollment statistics are presented and prior desegregation efforts, especially the 1965 Racial Balance Plan, are detailed, with special attention being given to the role of the State. Details of how controlled open enrollment works in Cambridge, a table showing the distribution of new students after implementation, and some conclusions about why certain schools attracted particular groups are then provided. Evidence is presented showing that, while some parents apparently made informed decisions, many did not indicate special reasons for choosing certain schools. Other topics arising from the new policy are then discussed, including fairness and the plan's impact on neighborhood schools and busing. Next, statistics documenting the plan's effectiveness in substantially desegregating Cambridge schools are presented. And finally, mention is made of the Cambridge plan's transferability to other systems. (KH)