The chapter begins by describing how PTSD is diagnosed, contrasting the ‘broad’, inclusive DSM formulations with the ‘narrow’ formulation focusing on core symptoms introduced in ICD-11. The ICD-11 distinction between PTSD and Complex PTSD is also described. We go on to consider why PTSD has been regarded as a disorder of memory, and the two signature changes consisting of vivid re-experiencing of the traumatic event in the present coupled with impaired voluntary recall of the event. Other aspects of memory affected in PTSD that are unrelated to the traumatic event include a general bias toward recalling negative rather than positive stimuli, verbal memory deficits, and difficulties in retrieving specific memories and suppressing unwanted memories. We discuss three prominent controversies, whether traumatic memories are ‘special’, whether traumatic events can be forgotten, and whether there is evidence for delayed onset PTSD. Contemporary theories of PTSD are then described including fear conditioning, neo-conditioning theories, the Ehlers and Clark cognitive model, and dual representation theory, all of which identify deficits in memory for context as central to the disorder. In the final section we discuss how traumatic memory changes with successful treatment and the likely mechanisms involved in psychological therapy for PTSD: Habituation/extinction, updating/reconsolidation, and metacognitive change
