The purposes of this study were to identify sources of self-confidence in athletes within the sport-confidence framework of Vealey (1986, 1988), develop a reliable and valid measure of sources of sport-confidence, and extend the conceptual framework of sport-confidence to include sources and test predictions within the expanded model. In Phases 1, 2, and 3 of the study, the preliminary conceptual basis for sources of sport-confidence was developed and initial psychometric evidence supported the factor structure, reliability, and validity of the Sources of Sport-Confidence Questionnaire (SSCQ) with 335 college athletes. In Phase 4, a confirmatory factor analysis supported the hypothesized nine-factor structure of the SSCQ using 208 high school basketball players as participants. The theoretical and practical significance of certain sources of confidence in building stable and enduring self-confidence and motivation in sport are discussed based on the study results.