Sex matters! Are there differences between the sexes when it comes to brain function and the behaviours that result? This volume attempts to answer this fundamental question. If the answer is 'yes' then this should impact upon our approach to treating mental illness in humans, and to modelling it in animals, as we look for aetiological and pharmacological solutions. This volume covers two main aspects of research into sex differences in psychopharmacology: preclinical research, and clinical work in this area. The first part of the volume deals with the preclinical research, and explains how male and female animals differ in their sexual behaviour, drug dependence, cognition, genetics and stress reactivity, with an introductory chapter explaining basic mechanisms of sex steroid action in the body and brain. The second part focuses on the importance of improved understanding of sex differences in our approach to the treatment of psychiatric illness. This includes illnesses such as autism, anorexia, depression, schizophrenia, and bipolar disorder. This volume will be of considerable interest to mental health professionals, including psychiatrists , nurses , allied health clinicians and pharmacists. It will also be helpful and important for preclinical researchers working in neuroscience, psychopharmacology and reproductive endocrinology. .