The author deals primarily with people who make a change in career orientation so distinct that the move requires at least a year of professional or graduate education. Chapters examine such topics as the changing nature of middle age; fields of study or endeavor (mainly social work, librarianship, elementary and secondary education, and other service professions) favored by middle aged students; reasons why men and women over 35 decide to enter or reenter professional or graduate school; and kinds of financial, academic, and family problems and adjustments experienced by such students. Seventeen case histories are presented to illustrate a wide diversity of motives, circumstances, and personal characteristics. Major findings include these: (1) most middle aged people who change careers were largely successful and satisfied in their previous work; (2) they tend to be dynamic individuals actively searching for new interests; (3) many people who return to work act with relatively little prior planning or guidance. Implications for education and guidance, theories of occupational choice, developmental psychology, and manpower policy formation, are discussed in the last chapter. An index and seven tables are included. (LY)