The progress in hydrogenation along with its introduction has been provided in this book. The sphere of catalytic hydrogenation is developing very rapidly, mirroring the vast area of chemical uses that can be improved by the simple utility of molecular hydrogen. Due to evolution in the characterization schemes and their use, our comprehension of the catalytic procedure and mechanisms occurring in homogeneous and heterogeneous catalysis has significantly increased. This book aims at providing a general outlook on the progress of hydrogen reactions. The book encompasses a set of reviews on the matters of heterogeneously and homogeneously catalyzed hydrogenation reactions. This book talks elaborately about the hydrogenation reactions in fine organic chemistry, hydrogenation reactions in ecological chemistry and inexhaustible power, and particular matters in hydrogenation.