A new barium copper phosphide compound, BaCu10P4, was synthesized by reacting stoichiometric amounts of the elements at 1200 degrees C for 24 h, BaCu10P4 crystallizes in the monoclinic space group C2/m, with unit cell dimensions a = 23.288(4) b = 3.9070(10), and c = 9.534(2) Angstrom and beta = 92.26(2)degrees (Z = 4). The structure can be described as consisting of chains of edge-shared Cu-4 tetrahedral prisms that are knitted together by P atoms. The structure is related to BaCu8P4, which can be described in a similar fashion. Temperature-dependent resistivity measurements indicate that BaCu10P4 is a metal. Extended Huckel band calculations are consistent with metallic character for BaCu10P4 through Cu-Cu interactions. Orbitals at the Fermi level show Cu-Cu bonding overlap. On the other hand, BaCu8P4 reveals extremely weak Cu-Cu interactions, but rather optimizes Cu-P bonding.