Iteroselectivity and regioselectivity are fundamentally different but complementary. Indeed, while the former leads to iteromers and the latter leads to regioisomers, several regioisomers may arise at each iteration of an iterative reaction. One simple example is the electrophilic aromatic substitution (SEAr) of functionalized benzene rings (Figure ). If one considers the Friedel-Crafts alkylation of anisole, it is usually fair to assume that it will generate ortho/para-alkylated anisoles with relatively good regioselectivity (ortho and para positions) and iteroselectivity (from mono to trialkylated anisoles). In contrast, the nitration of anisole expresses a similar regioselectivity (ortho and para positions favored) but the iteroselectivity is greatly enhanced due to the strong deactivation imparted by nitro groups leading mainly to mononitro anisole in mild reaction conditions. In this last case, the iteroselectivity is driven by electronic effects with a deactivating kinetic control.