The psychiatric interview is at the heart of psychiatry, since it provides the cornerstone of diagnostic assessment as well as being central to establishing a therapeutic relationship. This chapter, ‘Assessment’, describes the goals, principles, and practice of psychiatric interviewing. There is a detailed review of the various components of a full psychiatric assessment (the history, mental state examination, physical examination and investigations), as well as descriptions of how the assessment process is tailored to suit different situations (e.g. in emergency departments, in primary care, or in the community). The chapter proceeds to discuss how the information collected during the assessment is recorded and communicated. The chapter ends with a description of the major standardized assessment methods and ratings scales used in psychiatry.