Brain lesions cause memory to break down in several distinct ways in people. First, cortical lesions cause disturbances in short-term memory. Second, other cortical lesions disturb the retrieval of previously well-established semantic and episodic memories. Third, frontal cortex dysfunction seems to be related to a memory syndrome caused by a breakdown in the ability to plan and carry out elaborative processing. Fourth, and most explored, is the amnesic syndrome(s), caused by limbic system or diencephalic lesions. Other less-studied forms of memory breakdown almost certainly exist and some memory syndromes are compounded from these more basic deficits. Appropriate assessment of memory disorders must take this heterogeneity and complexity into account, and is important not only for clinical purposes but also to gain further insight into the precise nature of the different kinds of breakdown. The major theoretical and clinical requirements that such assessment procedures must meet are outlined.