This chapter contains sections titled: Introduction Diazonium-Diazo Equilibrium of Aliphatic Diazo Compounds Arenediazonium Ion ⇌ Diazohydroxide ⇌ Diazotate Equilibria Diazonium-Diazo Equilibria of Heterocyclic Diazonium Ions Reactions of Diazonium Ions with other Nucleophiles References