Dimagnesium copper, Mg₂Cu, M_r = 112.170, orthorhombic, Fddd (70), a = 5.275 (1), b = 9.044 (1), c = 18.328 (2) ./k, V = 874.3 (2) A₃, Z: 16, D_x = 3.41 g cm^-3, Mo Ka (A = 0.71073 A), /.i, = 101.145 cm^-1, F(000) -- 848, T = 293 K, R -- 0.034 (wR -- 0.031) for 17 refined parameters and 310 observed X-ray single-crystal reflections [F_o > 3~r(F_o)]. The refined parameters are consistent with the nonrefined parameters reported by Schubert & Anderko [Z. Metallkd. (1951), 42, 321-325]. The Mg2Cu structure type can be derived by a stacking of slabs that build up the A1₂Cu and Mg₂Ni structure types.