In the tradition of psychiatry, delusions have been seen as meaningless effusions of a diseased brain. Accordingly, psychological approaches were considered a waste of time. During the last several decades, researchers have taken on the challenge of understanding the psychological mechanisms that explain how delusional beliefs arise and are maintained. This understanding involves linking the increasingly well-known social and biological factors to individual dispositions that make a person vulnerable to misinterpreting experiences in a way that gives rise to delusions. The key-note will cover some of this research that draws on epidemiological, experimental and experience-sampling studies, and will derive its implications for psychological approaches to delusions.