This review summarizes the formation, structure, stability and reactions of aryliodonium zwitterions of closo-borate anions. The zwitterions are formed by regioselective aryliodination of closo-borates with ArI^II reagents and undergo efficient reactions with nucleophiles. Therefore, this tandem of reactions represents an effective regioselective activation of the B–H bonds in closo-borates towards nucleophilic substitution. (Image credit: Piotr Kaszyński.)