Often overlooked or incorrectly treated, post-traumatic stress disorder (PTSD) is a serious mental illness. Specialists often lack knowledge of its diagnosis and treatment, however, and this book is therefore intended to provide an overview. In the first part, the clinical pictures of the disturbances PTSD and complex PTSD (CPTSD) as defined in the ICD-11 and DSM-5 are explained and models of their development are described. The second part provides information on guideline-based diagnosis and provides an overview of various evidence-based therapeutic interventions and their similarities and differences. Current research developments are linked to clinical practice.