Homelessness is a complex problem that has existed in most societies for centuries. Far from solving this problem, in recent years an in-crease in the number of people homeless has been documented in Australia, the United States, Britain, and France. International studies reveal most homeless people have experienced trauma. Also, many suffer with posttraumatic stress disorder or PTSD as a result. Research on PTSD indicates that how a person thinks about a trauma is critical in determining who develops the disorder. It is possible that trauma experience combined with poor mental health are key to under-standing why some people remain homeless. This book reports on a study of homeless adults in Sydney. The aims of the study were to determine the extent of trauma experience, the prevalence of PTSD and its onset in relation to homelessness, and also to explore the role of post-trauma thoughts or cognitions in PTSD. This book will benefit any organisation that seeks to assist homeless people or people at risk of homelessness and will be of interest to mental health professionals who specialise in PTSD.