This book mainly focuses on the recent trends and sustainability challenges in the valorization of agro-wastes, emphasizing the role of microbial biotechnology. Processing of various kinds of agro-wastes such as lignocellulosic materials, food industry wastes, dairy wastes, etc., into several bioactive compounds, enzymes, biofuels, biogas, biofertilizers, nutraceuticals, nanoparticles, etc., will be discussed elaborately in more detail. This book investigates the theoretical and practical aspects of modern research regarding the valorization of agro-wastes through microbial technology. Moreover, the role of valorization research in circular bio-economy will also be addressed in this book.