William James, one of the founders of modern psychology, defined it in 1890 as ‘the science of mental life’. It is a science we can all relate to, as everyone has a mental life. ‘What is psychology? How do you study it?’ considers how psychology has been defined and the subjects of its study. Psychology is about the mind, or brain, and psychologists, working with other fields within cognitive science, now understand more about the structure of the brain. Psychologists also study behaviour. They are interested in the way organisms use their mental abilities to operate in the world. Complex interactions are the norm in psychology, rather than the exception.