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The metal-free reaction between diazo compounds and boronic acids has been established in recent years as a powerful C(sp3)–C bond-forming reaction. This account covers the recent advances in this area. First, the various synthetic applications of reactions with N-sulfonylhydrazones as a convenient source of diazo compounds is discussed. These transformations can be regarded as reductive couplings of carbonyl compounds. Also covered is the incorporation of other mild sources of diazo compounds in these reactions: diazotization of amines and oxidation of hydrazones. Finally, the development of sequential and cascade processes is presented. 1 Introduction 2 Early Work: Reactions Between Alkylboranes and Diazo Compounds or N-Sulfonylhydrazones 2.1 Reactions Between Alkylboranes and Diazo Compounds 2.2 Reactions Between Alkylboranes and N-Sulfonylhydrazones 3 Reactions of N-Sulfonylhydrazones and Diazo Compounds with Aryl and Alkylboronic Acids 3.1 Reactions of Arylboroxines with Diazo Compounds 3.2 Reductive Couplings of N-Sulfonylhydrazones with Aryl- and Alkylboronic Acids 3.3 Three-Component Reactions Between α-Halotosylhydrazones, Boronic Acids and Indoles 4 Reactions of N-Tosylhydrazones with Alkenylboronic Acids 5 Synthesis of Allenes by Reactions with Alkynyl N-Nosylhydrazones 6 Reactions with Diazo Compounds Generated by Diazotization of Primary Amines 7 Reactions with Diazo Compounds Generated by Oxidation of Hydrazones 8 Reactions with Trimethylsilyldiazomethane 9 Cascade Cyclization Reactions with γ- and δ-Cyano-N-tosylhydrazones 10 Summary and Outlook [ABSTRACT FROM AUTHOR]