? The catalytic decomposition of diazo compounds and the subsequent insertion of a carbene group into the C-H bond constitute one of the very few examples of effective catalytic functionalization of hydrocarbons. This transformation has been achieved with rhodium-, copper-, silver- and gold-based catalysts under mild conditions. Recently, the catalytic carbenoid insertion in non-conventional media has attracted attention, because such reactions offer more environmental-ly friendly organic synthetic methodologies. In this review, recent reports on this topic will be summarized.