This is the updated and thoroughly revised edition of the popular textbook, fondly dedicated to the memory of Dr CC Chatterjee who had written the book in the Independence era of country in 1948. Dr Chatterjee was the faculty at Calcutta Medical College. This book was widely read throughout the country and South East Asia for over four decades and helped medical and paramedical students to have firm understanding of the functional aspects of human body. Dr Chatterjee passed away in 1984 but his book still remains in the minds of millions of readers who read it with passion. He wrote a complete integrated physiology textbook with anatomy and biochemistry encompassed altogether in the era when there were no computers or any advance technology for printing. The integrated approach of incorporating anatomy, physiology and biochemistry in this single textbook was marveled by all academicians and was one of the salient features of the book of all the eleven editions up to 1984.Prof Nitin Ashok John, as editor of the book, took the challenge of editing the eleventh edition to the prescribed existing syllabus and twelfth edition was brought out in 2018. As Medical Council of India recommended the competency based curriculum, the thirteenth edition was designed to match the newly designed curriculum. As inputs flowed in from academicians across the country, these were taken into consideration and the fourteenth edition of the book was written as per the National Medical Commission, Competency Based Curriculum. The fifteenth edition features a host of modifications and innovations brought into sparkle it as a popular textbook for undergraduate students of medical sciences, dental sciences, Ayush courses, and other paramedical and allied health sciences courses.Salient Features of Fifteenth Edition-˜… Presents simplified and comprehensive text to make it easy to understand, and to give a clear conceptual understanding of the subject to the students.˜… Provides completely integrated physiology with clinical orientation, apart from horizontal integration.˜… Covers comprehensive applied and comparative physiology.˜… Includes clinical case scenarios and recent advances.˜… Incorporates a separate section on Multiple Choice Questions and Answers for viva voce and theory examinations.˜… Attempts to serve as a guide for university examinations and job interviews.˜… Designed for the candidates appearing in NEET PG, ExiT Examinations, USMLE and PLAB.˜… Carries updated examination-oriented questions.˜… Oriented towards quick understanding and recapitulation of basics.˜… Characterises historical features and scientific findings depicted appropriately in the text.