We show that Dranishnikov's asymptotic property C is preserved by direct products and the free product of discrete metric spaces. In particular, if G and H are groups with asymptotic property C, then both G×H and G * H have asymptotic property C. We also prove that a group G has asymptotic property C if 1 → K → G → H → 1 is exact, if asdim K < ∞, and if H has asymptotic property C. The groups are assumed to have left-invariant proper metrics and need not be finitely generated. These results settle questions of Dydak and Virk [15], of Bell and Moran [5], and an open problem in topology in [23].2010 Mathematics Subject Classification. 54F45 (primary), 20F69 (secondary).