I present seven empirical studies that investigate two main themes regarding two main approaches of optimism: explanatory style and dispositional optimism. The first theme incorporates measurement issues and conceptual ideas of optimism and the second involves optimism interventions on depressive symptoms. In Study 1 I explored the potential psychometric structure of causal attributions and dispositional optimism. Attributions may be best viewed as reflecting large differences in cognitive style, and smaller independent positive- and negative-event biases. For dispositional optimism, a two-factor model was supported. Study 2 examined correlations between optimism and the Five-Factor Model of personality. Dispositional optimism and explanatory style had similar association patterns with personality, although there were some differences. Study 3 tested and supported a model in which dispositional optimism mediates the link between explanatory style and psychological well-being. Study 4 compared the levels of optimism expression in two ethnic groups, finding that Mainland Chinese participants were more optimistic and less pessimistic than White British. Study 5 examined attributional biases and found that individuals show more optimistic biased style for themselves than for other people. Studies 6 and 7 tested effectiveness of optimism interventions on depressive symptoms. It demonstrated that self-monitored optimism interventions on a daily basis could effectively reduce depressive symptoms and increase optimistic explanatory style. Taken together, the studies replicated some previous investigations regarding measurement issues and conceptual ideas of optimism, and explored novel approaches to examining the essence of attributional bias and effectiveness of optimism interventions in depression treatment. My investigation of attributional bias is the first to test this idea using new and comparable measures of attributions. Practicing self-administered optimism interventions is, to my knowledge, also the first time these interventions have been applied in a sample with mild-to-moderate depressive symptoms. This may provide an easily monitored and low-cost alternative to traditional treatments of depression.