Intermittent catheterization (IC) is a widely used technique for emptying the bladder, first recorded in 1000?bce. This article describes the normal anatomy and physiology of bladder filling and emptying, and discusses the reasons why emptying may be incomplete. Incomplete emptying usually has a neurogenic or obstructive cause, leading to symptoms such as frequency, urge incontinence and urinary tract infection. IC may be carried out for several reasons: as an acute intervention for transitory problems with bladder emptying; to enable the instillation of drugs into the bladder; or as a long-term intervention where there is a regular post-void residual volume of more than 100?ml. Ideally, the patient intermittently catheterizes his/her own bladder, but a relative or healthcare professional may carry out this task. Some patients have specific requirements and problems, and case studies are presented to illustrate how these problems may be resolved.