The research literature on types of student retention, correlates of retention, and action strategies to improve retention is reviewed. Retention or student persistence can be assessed in terms of completion of a degree of certificate, a program but not a degree, or a term or course. Retention may also be persistence to attain a personal goal but short of a degree or a certificate. One type of retention study is designed to determine the characteristics and attitudes that are common among students who persist and among those who drop out. Research has indicated both student and institutional correlates of retention, and a number of theories have postulated that the interaction and fit between students and their institution are important in explaining retention and attrition. A second type of retention study focuses on the practical application of retention strategies and their effectiveness in improving retention. A number of these studies are reviewed, beginning with the "What Works in Student Retention?" study (WWISR), the first comprehensive, national survey of action programs designed to improve retention. The action literature is discussed under two major headings: single-facet retention approaches and multifaceted approaches to improving retention. Twelve kinds of single-facet retention approaches are identified, and their effects on student retention are summarized: admissions and recruiting, advising, counseling, early warning and prediction, exit interviews, extracurricular activities, faculty and staff development, curriculum development, financial aid, housing, learning and academic support, orientation, and policy change. A bibliography is included. (SW)