Team efficacy beliefs, defined as a team’s collective sense of its ability to perform a specific task, are an important factor in predicting team performance, and have been shown to influence team goals and member commitment. However, to date little research has focused on how efficacy beliefs develop within teams. This study used a longitudinal approach, following Gibson (2003), to understand the process by which team efficacy beliefs, and through these other variables such as goal setting, commitment, and ultimately team performance, develop and are impacted by leader behavior. This study proposes that the implicit and explicit messages communicated by emergent team leaders through their behavior have a large impact on the development of team efficacy beliefs. Qualitative analysis of longitudinal data uncovered eight themes of behavior expressed by emergent team leaders which were associated with higher levels of team efficacy and team performance.