The use of Mo V reagents, and in particular MoCl 5 , in organic synthesis is surveyed. The oxidative treatment of aromatic substrates is the most common application. The unique properties of these reagents are due to their high oxidative power combined with exquisite Lewis acid properties. In several examples Mo V reagents outperform other common oxidative coupling reagents. C-C bond formation through inter-and intramolecular oxidative coupling can lead to selective formation of five-to eight-membered ring systems. Mechanistic investigations of the courses of reactions involving Mo V reagents and aromatic substrates indicate that radical cations are initially