Optimism can be defined as positive generalised outcome expectancies and has been shown to act as a protective factor against somatic and mental health problems. Numerous studies report an association between optimism and enhanced coping strategies, lower levels of distress and depression, lower risk of mortality, slower disease progression, and better psychological adjustment to a diagnosis and treatment of a severe disorder. Although these findings indicate an important role of optimism on well-being, very little is known about the origins of individual differences in optimism. This book presents research in the study of optimism including the relationship between dispositional optimism and musculoskeletal pain, the phenomenological and statistical relationships between optimism and sense of coherence and self-efficacy and genetic influences on optimism and mental health.