Diazo compounds are versatile substances with diverse transformations in organic synthesis and other fields. Studies of diazo compounds have been ongoing for a very long time but still attract significant attention within the organic chemistry community, with new papers related to diazo compounds appearing at a daily pace. Over the past twenty years, there have been over fifty reviews and accounts related to the reactions of diazo compounds, but most of them cover limited aspects of diazo compounds. In addition to organic synthesis, diazo compounds have found applications in interdisciplinary fields such as material sciences, chemical biology and also polymerization.In this comprehensive book, the authors cover the most recent advances in the fields related to diazo compounds, including the application of donor-acceptor carbenes, carbene-based cross-coupling reactions and polymerizations, as well as the breakthrough in catalytic asymmetric carbene O-H, S-H, and N-H bond insertions. They also cover the application of flow chemistry in diazo reactions. The authors aim to provide a contemporary and comprehensive review for investigators engaged in or with interest in diazo compounds to boost further developments in this fascinating field.