The i.r., ¹H n.m.r. and electronic spectra of the new diphenylphosphine complexes of the copper(I) halides [Ph₂PHCu·X]₄, [(Ph₂PH)₂Cu·X]₂, (Ph₂PH)₃Cu₂Cl₂, and (Ph₂PH)₃Cu·X are reported and discussed. Marked differences in the electronic spectra were used to monitor the dissociation of these species in solution. There is no evidence for an intermediate species between (Ph₂PH)₃Cu·X and (Ph₂PH)Cu·X during solution decomposition, despite the isolation of the intermediate stoicheiometries in the solid state.