Abstract: The crystal structure of szenicsite, Cu₃MoO₄(OH)₄, orthorhombic, a = 8.5201(8), b = 12.545(1), c = 6.0794(6) Å, V = 649.8(2) ų, space group Pnnm, Z = 4, has been solved by direct methods and refined by least-squares techniques to an agreement index (R) of 3.34% and a goodness-of-fit (S) of 1.11 for 686 unique observed [|4| ⩾ 4σ_F] reflections collected using graphite-monochromated Mo-Kα Xradiation and a CCD area detector. The structure contains three unique Cu²⁺ positions that are each coordinated by six anions in distorted octahedral arrangements; the distortions of the octahedra are due to the Jahn-Teller effect associated with a d⁹ metal in an octahedral ligand-field. The single unique Mo⁶⁺ position is tetrahedrally coordinated by four O²⁻ anions. The Cu²⁺B₆ (Ф: unspecified ligand) octahedra share trans edges to form rutile-like chains, three of which join by the sharing of octahedral edges to form triple chains that are parallel to [001]. The MoO₄ tetrahedra are linked to either side of the triple chain of Cu²⁺Ф₆ octahedra by the sharing of two vertices per tetrahedron, and the resulting chains are cross-linked through tetrahedral-octahedral vertex sharing to form a framework structure. The structure of szenicsite is closely related to that of antlerite, Cu₃SO₄(OH)₄, which contains similar triple chains of edge-sharing Cu²⁺Ф₆ octahedra.