We rely on prospective memory (PM) to carry out intended actions at an appropriate time in the future. This ability is very important for day-to-day functioning, for example, remembering to take medication, attend appointments and pay bills. The literature covering the topic of PM has increased exponentially in the past 20–30 years. This paper will describe this relatively novel form of memory and discuss the debilitating effect PM deficits have on everyday living. It will also examine the populations who experience significantly more frequent and severe PM impairments and explore the causes and mechanisms of PM impairments by reviewing behavioural, clinical, genetic and neuroimaging studies. The paper will conclude by discussing the latest research into ways of treating PM impairments in clinical populations. Where applicable, examples of research conducted by the author and his colleagues will be used to illustrate these topics.