This book has been designed to provide relevant and the best study material for the preparation of Indian National Biology Olympiad (INBO) conducted by the Homi Bhabha Centre for Science Education. The book is equally useful for National Standard Examination in Biology (NSEB) and other Biology Olympiads. This book has been designed to give the students an insight and proficiency into almost all the areas of Biology asked in various Biology Olympiads. The present book has been divided into eight chapters namely Bio systems Cell Biology Genetics and Evolution Plant Anatomy Physiology and Reproduction Animal Anatomy Physiology and Reproduction Ecology and Environment Ethology and Biology in Human Welfare each sub-divided into number of topics as per the syllabi of the INBO. The book contains complete theory exactly on the pattern of INBO and NSEB. Ample number of solved examples designed according to the pattern and the level of Indian National Biology Olympiads have been provided in the book. Also unsolved practice problems for both INBO and NSEB have been provided in the book to help aspirants revise the concepts that are asked in the Biology Olympiads. Chapter wise coverage of all the questions of INBO and NSEB from 2000-2018 has been provided in the book. Each chapter has two level exercises divided according to NSEB and INBO. Problems from recently held Olympiads have also been given in the book. The book also contains 2014-2018 solved papers of NSEB and INBO with detailed and authentic solutions for comprehensive understanding of the concepts on which the questions were based. As the book contains ample study as well as practice material it for sure will help aspirants score high in the upcoming Indian National Biology Olympiad 2018.