Immunohistochemistry (IHC) has emerged as an indispensable tool in the diagnosis and characterization of oral tumors, providing critical insights into their behavior, origins, and prognosis. This book comprehensively explores the principles, methods, and applications of IHC in the context of oral tumor diagnosis. Beginning with an overview of antigen-antibody interactions and the types of antibodies utilized, the book delves into the various labeling methods and techniques employed in IHC protocols. Additionally, it discusses the historical context of IHC, tracing its evolution from its inception to its current widespread use in biomedical research and diagnostics.The book explores the diagnostic utility of various markers in differentiating between different types of tumors within the head and neck region. It highlights the importance of accurate classification and treatment planning facilitated by IHC, particularly in challenging cases where traditional staining techniques may fall short. By elucidating the principles, methodologies, and clinical applications of IHC, this book serves as a comprehensive resource for researchers, pathologists, and clinicians involved in diagnosis.