Methods for the formation of diazo compounds, hydrazones, and imines substituted with a heteroatom at nitrogen are reviewed. For formation of hydrazones, reaction of a carbonyl compound with a hydrazine remains the most popular method, although there has been a significant increase in the reports of functionalization of hydrazones, both at the hydrazone carbon and the α-carbon. Most of these methods are asymmetric reactions of proline-derived hydrazones. Other methods for the formation of hydrazones have been used only occasionally, and include reduction of diazo compounds and conjugate addition to azo compounds. Metallated imines are prepared by a variety of methods, depending on the choice of metal. N-Lithiated imines are generally prepared by addition of organolithium reagents to nitriles, although these compounds are seldom isolated. N-Silylimines are most conveniently prepared by addition of a bis-silylamine to a carbonyl compound. These two classes of substituted imines have been used to prepare a range of other heteroatom-substituted imines by substitution of either lithium or silicon. Diazo compounds are most commonly prepared by diazo transfer to a methylene group flanked by one or more electron-withdrawing groups. Sulfonyl azides are widely used to achieve this transformation, although a range of reagents and other modifications have been used in individual cases. In recent years, the versatility of the diazo group has been demonstrated by a number of new reactions, which feature elaboration of diazo compounds either at the diazo-carbon or elsewhere. Less commonly, oxidation of hydrazones and Bamford–Stevens reaction of sulfonylhydrazones have been used to prepare diazo compounds. A hydrogen atom on a diazo-carbon is readily removed, and this chemistry has also been used to access a range of compounds bearing heteroatoms at the diazo carbon.