Mastitis is one of the most significant diseases affecting sheep production worldwide, causing substantial economic losses through reduced milk yield and quality, increased treatment costs, premature culling, impaired lamb growth, and occasional ewe mortality. It also represents an important animal welfare issue due to the pain and suffering experienced by affected animals. Ovine mastitis is a multifactorial disease involving interactions among infectious pathogens, host factors, environmental conditions, and management practices. Numerous microorganisms, including Staphylococcus aureus, coagulase-negative staphylococci, Mannheimia haemolytica, streptococci, coliform bacteria, and mycoplasmas, contribute to disease occurrence. Effective control therefore requires integrated, evidence-based approaches that combine prevention, early detection, and appropriate management. Recent advances in mammary gland biology, immunology, microbiology, diagnostics, and precision livestock technologies have improved our understanding of mastitis and enhanced disease control strategies. At the same time, concerns regarding antimicrobial resistance have emphasized the importance of sustainable flock health programs focused on biosecurity, milking hygiene, nutrition, genetic selection, and prudent antimicrobial use. This handbook was developed to provide a comprehensive and scientifically grounded reference on ovine mastitis. It brings together current knowledge on mammary gland biology, epidemiology, etiology, pathogenesis, diagnosis, treatment, prevention, and emerging technologies, while emphasizing practical applications for field conditions. Designed for veterinarians, students, researchers, animal health professionals, extension specialists, and sheep producers, this handbook aims to bridge the gap between scientific research and practical flock management, serving as both an educational resource and a practical guide for improving udder health and productivity in sheep.