This study estimates the proportion of transfer students (those who transfer from one college to another) in various categories and explores some potential explanations of the transfer phenomenon. The data base used was drawn from the base-year and the first and second followup data of the National Longitudinal Study of the High School Class of 1972. The extent of transfer in terms of percentages and estimated numbers of various transfer groups is discussed and the differences in transfer rates among subgroups are described (e.g., groups defined by sex, race, and levels of ability and educational aspiration). The differences between transfers and nontransfers in four-year and two-year institutions are examined and include comparisons between transfers and persisters, and between tranfers and withdrawals. Vertical transfers (e.g., students who moved from two-year to four-year colleges) are compared with four-year native students on background variables, financial aid status, satisfaction with college education, and academic performance. Tabulations of students' self-reported reasons for changing schools are presented separately by type of transfer and type of college. Three hypotheses are related to reasons for transferring; these center on the issue of an incongruency between the student and the institution. The major findings and implications are summarized. (SPG)