This chapter explores what confidence is and in particular consider the different theoretical conceptualizations that currently exist. It explores on overconfidence and robust/resilient confidence, and also considers the implications for practice. Three major conceptualizations of confidence have been suggested in the broader psychology literature: self-efficacy, self-confidence, and sport confidence. Self-efficacy theory was first introduced by Bandura to both explain and adapt human behaviour. Self-efficacy was defined by Bandura as 'beliefs in one's capabilities to organize and execute the course of action required to produce given attainments'. Self-confidence is proposed to be context-specific to relevant tasks and it is suggested that some individuals can display this feature through a wide range of activities. Vealey developed a sport-specific construct of self-confidence termed 'sport confidence defined as 'the belief or degree of certainty about one's ability to be successful in sport'. The development of robust self-confidence appears key in achieving long-term performance success.