To effectively address the needs of second language (L2) learners in college writing courses, many postsecondary institutions, especially those located in cities with high concentrations of immigrants, offer college-level courses for L2 students. Such courses include noncredit English language courses in an intensive English program, developmental or basic writing courses created with native speakers in mind, and credit-bearing first-year and advanced composition courses designed specifically for L2 students. The existence of a variety of course options for L2 writers signals recognition by writing programs of the varying needs that L2 students may have; determining which courses are most suitable for certain L2 learners, however, remains a complex issue. In fact, in recent years several practitioners working with L2 writers have called into question the custom of treating all L2 learners as one group, defined primarily by their non-native speaker status. Indeed, anyone who has taught classes with large numbers of L2 learners can attest to the great deal of heterogeneity within the L2 population in US writing programs. While a body of research investigating differences among various types of L2 learners has begun to emerge, there remains a very limited amount of empirical evidence supporting the need for separate courses for different L2 learners. This article reviews various frameworks for defining second-language learner groups, as described in the literature, and summarizes relevant empirical studies based on these frameworks.