This book provides researchers in the fields of organic chemistry, organometallic chemistry and homogeneous catalysis with an overview of recent developments in the applications of reactions involving carbene and nitrene intermediates directed to the synthesis of heterocyclic compounds. Multiple pathways through which diverse heterocyclic compounds are accessed occur from a variety of carbene and nitrene precursors through C-H/X-H insertions, cycloadditions, ylide transformations, rearrangements, and cascade reactions. Catalytic processes that form metallo-carbenes and nitrenes offer unparalleled chemo-, regio-, and stereo-selectivities. Insights are provided into the scope of these methodologies and the inherent control of catalyst ligands on reaction selectivities.