Pharmacology is a dynamic and multifaceted field that lies at the heart of modern healthcare. It encompasses the study of how drugs interact with biological systems to produce therapeutic effects, as well as their mechanisms of action, pharmacokinetics, and therapeutic uses. As the landscape of pharmacotherapy continues to evolve, it is essential for healthcare professionals to have a comprehensive understanding of pharmacological principles and their clinical applications. This book, "Pharmacology – Theory," is crafted with the aim of providing students, educators, and practitioners with a thorough and accessible resource that explores the fundamental concepts and practical aspects of pharmacology. Designed as a comprehensive guide, it covers a wide range of topics, from the basic principles of drug administration to the pharmacology of various organ systems and drug classes. The journey through pharmacology begins with an exploration of the fundamental concepts in drug administration, absorption, distribution, metabolism, and excretion. Understanding these processes is crucial for optimizing drug therapy and ensuring patient safety. Building upon this foundation, the book delves into the pharmacology of drugs acting on the peripheral and central nervous systems, cardiovascular system, blood and blood-forming organs, respiratory system, gastrointestinal tract, and kidney. Each section of the book is meticulously structured to provide a detailed examination of the pharmacological principles underlying the therapeutic use of drugs within specific organ systems. In addition to discussing the pharmacological actions, indications, contraindications, and dosages of various drug classes, the book also highlights the clinical relevance of pharmacological concepts through the integration of case studies and real-world examples. Special attention is given to the unique considerations and challenges encountered within the Indian healthcare system. By incorporating pertinent examples and case studies from the Indian context, we aim to enhance the relevance and applicability of pharmacological principles for Indian pharmacy professionals, students, and educators.