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.