Polycystic ovary syndrome (PCOS) is a significant public health issue with reproductive, metabolic and psychological features. PCOS is one of the most common conditions. Women with PCOS present with diverse features including psychological (anxiety, depression, body image), reproductive (irregular menstrual cycles, hirsutism, infertility and pregnancy complications) and metabolic features (insulin resistance (IR), metabolic syndrome, prediabetes, type 2 diabetes (T2D) and cardiovascular risk factors). Diagnosis and treatment of PCOS remain controversial with challenges defining individual components within the diagnostic criteria, significant clinical heterogeneity generating a range of phenotypes with or without obesity, ethnic differences and variation in clinical features across the life course. In this volume, we provide the reader with up-to-date information about what is currently known about PCOS and what are the challenges still facing the research and clinical care communities.