This book has been written with the intention to cater to the needs of Medical and Science undergraduate students of the University of Kashmir and the University of Jammu in addition to other Indian universities for having a good understanding of the basics of human physiology. The book has been written to meet the requirements of the users in accordance with their level. The subject matter follows a conventional pattern along with a practical approach. The language throughout is simple, scientifically appropriate, with instructive illustrations, and logical and comprehensive coverage. The aim throughout has been to develop a sense of proportion towards the subject and a grasp of its fundamentals, which one may not acquire easily from larger books. We hope this book will not only serve the purpose of undergraduates for whom it is intended but also will be used by allied and higher classes. Constructive criticism and suggestions from my learned colleagues, academicians, and students is always welcome for its further improvement.