Self-concept clarity (SCC) references a structural aspect of the self-concept: the extent to which self-beliefs are clearly and confidently defined, internally consistent, and stable. This article reports the SCC Scale and examines (a) its correlations with self-esteem (SE), the Big Five dimensions, and self-focused attention (Study 1);(b) its criterion validity (Study 2); and (c) its cultural boundaries (Study 3). Low SCC was independently associated with high Neuroticism, low SE, low Conscientiousness, low Agreeableness, chronic self-analysis, low internal state awareness, and a ruminative form of self-focused attention. The SCC Scale predicted unique variance in 2 external criteria: the stability and consistency of self-descriptions. Consistent with theory on Eastern and Western self-construals, Japanese participants exhibited lower levels of SCC and lower correlations between SCC and SE than did Canadian participants.