Ideational apraxia is a rare behavioural disturbance observed in patients with a lesion in the posterior part of the hemisphere dominant for language. The main feature is an impairment in carrying out sequences of actions requiring the use of various objects in the correct order necessary to achieve an intended purpose. The syndrome cannot be explained as being due to paresis, aphasia, impaired visual recognition, mental deterioration or a combination of these disorders. It must be considered as a higher order motor disturbance. Perservation plays an important role but can not explain the syndrome. Evidence is presented to suggest that ideational apraxia is a disturbance in the conceptual organization of actions. Lines of future research are indicated.