The almost unexplored four-membered heterocycles azetidines, represent a particularly interesting class of molecules, among the family of saturated nitrogen heterocycles. Although often challenging to synthesize, substituted azetidines strongly attract chemists because of their importance in catalysis, stereoselective synthesis and medicinal chemistry. This review aims to give a brief summary of modern developments in direct metal-based functionalization of the azetidine ring, focusing on the regio- and stereoselectivity of these reactions, as well as on some useful synthetic applications. It will be highlighted, in particular, how an interplay of factors such as structure, substitutions at both nitrogen and carbon atoms and coordinative phenomena deeply influence the reactivity of the corresponding metallated species, paving the way for easy planning a site-selective functionalization of azetidines.