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Our understanding of the mechanisms underlying very long-term memory impairments remains rather limited. The aim of this thesis is to clarify the nature of various distinctive forms of very long-term memory disorder and to shed light on the mechanisms that give rise to these syndromes. Chapter 1 provides a review of the relevant literature. Chapter 2 presents three sets of studies examining the nature and extent of retrograde amnesia following damage to temporal lobe and diencephalic structures. The extent to which medial temporal lobe structures are involved in the retrieval of autobiographical event memories across the lifetime is considered. The findings from these studies suggest that the hippocampal complex is critical to the ability to mentally re-experience or 'replay' events over a very extended period of time and probably as far back as childhood. These findings provide support for Multiple Trace Theory (Nadel and Moscovitch, 1997), and are less supportive of predictions derived from the Standard Consolidation Model of memory (Squire and Alvarez, 1995; Murre, 1996). Chapter 3 is concerned with (i) the circumstances under which extensive retrograde amnesia may occur in the absence of anterograde memory deficit and (ii) the dissociation of episodic and semantic retrograde amnesia. Two cases are studied. The first case, a patient with cerebral vasculitis, presented with a severe impairment in autobiographical episodic memory, with normal anterograde memory. The second case presented with a progressive impairment in her ability to recognise familiar faces and a loss of knowledge of people in the presence of intact autobiographical memory. Although the findings from these cases highlight the dissociation of episodic and semantic memory, it is argued that in the undamaged human brain there is a complex and dynamic interaction between the experiential and factual components of long-term memory. Chapter 4 presents two studies of very long-term anterograde memory.