In this book, recent advancements in the heterocycles functionalization by using different transition metals have been described. Heterocycles are the central point mainly in drug discovery and various other fields. The ease with which one can functionalize these scaffolds mainly accounts for the whole process output. In the last three decades, C-H activation has emerged as the sustainable and economic way to functionalize the heterocycles. Numerous catalytic methods have been developed and are being developed by applying mainly transition metals. The books main emphasis has been given to mechanistic aspects and the application of developed methodologies for the functionalization of natural scaffolds. The book is useful for researchers who are working in the area of C-H activation/functionalization in academia and industry.