Ru(II) complexes, such as Cp*RuCl(PPh₃)₂, regioselectively catalyze 1,3-dipolar cycloaddition of organic azides and alkynes. Diversely functionalized 1,5-disubstituted triazoles are usually obtained in good to excellent yield after heating the reaction mixture at 50 – 80 ^oC for several hours. Furthermore, internal alkynes also participate in the catalysis, producing 1,4,5-trisubstituted 1,2,3-triazoles. Thus, the ruthenium system complements the copper-catalyzed azide-alkyne cycloaddition, providing facile access to wide range of 1,2,3-triazoles with different substitution patterns.