This book on Diagnostic Pathology Techniques and Applications serves as a comprehensive guide that explores the fundamental principles, evolving methodologies, and diverse applications integral to the field of diagnostic pathology. Designed to bridge the gap between traditional pathology practices and modern technological advancements, it provides readers with an in-depth understanding of how various diagnostic tools are employed to accurately identify and characterize diseases. Throughout the chapters, the book delves into the classical histopathological techniques that have long been the backbone of pathological diagnosis, including tissue processing, staining methods, and microscopic evaluation. It carefully elucidates the critical role these foundational approaches play in the initial detection and classification of pathological changes in tissues and cells. Beyond the traditional scope, the book emphasizes the integration of advanced techniques such as immunohistochemistry, molecular diagnostics, and cytology, which have transformed the accuracy and specificity of pathological diagnoses. It thoroughly discusses how these innovations have expanded the pathologist’s toolkit, enabling more precise identification of disease subtypes and molecular alterations, which are essential for personalized treatment strategies. Special attention is given to the applications of these techniques in various medical disciplines, including oncology, infectious diseases, genetic disorders, and autoimmune conditions, highlighting their clinical relevance and impact on patient management.