Optimism and pessimism are complementary, but opposing, dispositions. In general, optimists consistently expect good outcomes and pessimists consistently expect bad outcomes. These variations in human behaviour have profound mental and physical implications. The aim of the present work is to provide an overview of the psychology of pessimism. It is composed of four sections: how are optimism and pessimism measured, what is the relationship between optimism and pessimism, what is the relationship between optimism-pessimism and health, and, what are the biology and chemistry of...