Using both proficiency tests and self-assessment measures, this study investigated (a) whether 3 subgroups of Japanese heritage language (JHL) learners would demonstrate language behaviors distinctively different from those of traditional Japanese as a foreign language (JFL) learners, and (b) which domains of language use and skills would specifically identify such differentiation. Statistical analyses of data collected from 185 JFL and JHL students aged 17-22 indicated that there were striking similarities between the JFL Learner group and 2 JHL groups (JHL students with at least 1 Japanese-speaking grandparent but without a Japanese-speaking parent as 1 group, and JHL students of Japanese descent without either a Japanese-speaking parent or grandparent as the other). In contrast, another group of JHL students (those with at least 1 Japanese-speaking parent) proved to be substantially different from other groups in (a) grammatical knowledge, (b) listening and reading skills, (c) self-assessed use/choice of Japanese, and (d) self-ratings of a number of can-do tasks (Clark, 1981) that represented a wide range of abilities.