This references book is launched in two volumes- A reference book on Catalysis Volume – I Special Reference to catalytic reactions and applications, A reference book on Catalysis Volume – II Special Reference to metal complexes & Hydrogenation. The Intension of this book is to present some more aspects of catalysis viz.; use of different metal complexes as homogeneous catalyst towards the dihydrogen reduction of various organic substrates. The behavior of different metal complexes as catalyst may be different in various aspects. To obtain more efficient and industrially applicable catalyst, modifications are incorporated in this volume. Use of these modified complexes as catalyst towards the reduction of organic substrates is also included. The key features are- Synthesis, characterization and immobilization of the ligands and their complexes. Use of homogeneous complexes as catalysts towards hydrogenation of organic substrates under normal and high pressure of hydrogen. Use of Immobilized complexes as catalyst towards hydrogenation. This volume of the book is related to the synthesis, characterization & the catalytic activities, so it may beneficial for PG and Ph.D researchers.