Carbodiimides (RN=C=NR) have proved, over the last 130 years, to be versatile reagents and they rank as one of the most important classes of sources of nitrogen in organic chemistry.This presentation will focus on our recent development on the metal-promoted or-catalyzed carbodiimide chemistry to construct various aza-heterocycles.Furthermore, mechanistic studies are carried out by the isolation and structural characterization of the important reaction intermediates.