This book is an attempt to provide an account of biomass recalcitrance and available physical and chemical methods for biomass pretreatment and hydrolysis. Its focuses on understanding the critical role of enzymes in the development of integrated biorefinery. The book also presents an overview of the utilization of waste biomass as a support system for enzyme immobilization for easy recovery and reuse for multiple cycles. strategies where enzymes can be used. The book also attempts to understand how enzymes can play a vital role in waste valorization for energy and biomaterial production. Further, the book will present an overview of how advanced technologies such as omics and in-silico approaches can help in understanding the chemistry affecting recalcitrance and the mechanism of enzyme catalysts in their bioconversion. An understanding of the life cycle assessment of waste biomass biorefinery will be needed before its implementation. The book will serve as additional reading material for undergraduate and graduate students of energy studies, chemical engineering, applied biotechnology, and environmental sciences. This book is of interest to academicians, scientists, environmentalists, and policymakers.