The book ‘Biology of chordates’ has been written on the overwhelming demand of the students pursuing M.Sc. from different universities of India. The book aims to cater for the students of final year in their masters. Divided in 25 chapters, the book contains objective, short and long type questions at the end of each chapter. This enterprise is an effort to write an easy-to-understand book in simple language for the students. Origin, evolution and adaptive radiation of chordate groups have been simplified avoiding complications for the benefit of our young readers. Illustrations have been specially designed with utmost care, accuracy and keeping in conformity with their textual description. With recent studies in the phylogeny of chordates, some long-overdue modifications of animal classification have become necessary. They all have been adopted in the text at appropriate places, to bring them up to date. The book is the outcome of author`s deep devotion to the study of chordate taxonomy throughout a long and sustained classroom teaching in a career spanning over more than 25 years at various government colleges of Rajasthan, India. He was awarded with “The state level award-2020” by the Government of Rajasthan, in Jaipur. He was also awarded with “The best academician of the year-2021” by the Center for Educational Growth and Research (CEGR), New Delhi. He trust the utility of the book has been greatly enhanced by the modifications made.