Building upon extensive prior research by the investigators' expert team, the proposed study will examine the effects of Imaginal Rescripting (IR) as a stand-alone single session intervention for social anxiety disorder (SAD). IR is a short but effective cognitive behavioural intervention, which guides patients to change their memories of past socially painful events. The purpose of the study is to examine the effects of IR in relation to two comparison conditions and by doing so also provide much-needed experimental evidence in clinical participants to distinguish between competing theories of treatment mechanisms. Does IR work by altering the content of the memory or simply by changing its meaning or impact, or both? If modifying memory content is important, does IR improve access to more positive memory details that compete with the original negative ones for activation in subsequent contexts or eradicate elements of the original traumatic memory, perhaps via the disruption of memory reconsolidation? The study will take advantage of the recent development and validation of the Waterloo Images and Memories Interview, which enables researchers to measure the accessibility, subjective appraisals, and narrative content of autobiographical memories (and associated mental images) that participants report experiencing. One particularly important outcome generated by the WIMI for the present study involves having trained coders count the number of "episodic" vs. "non-episodic" negative and positive autobiographical memory details present in participants' reported narratives over time.