Let Ro be a skew field, or more generally, a finite product of full matrix rings over skew fields. Let (RX)XEA be a family of faithful Rorings (associative unitary rings containing RO) and let R denote the coproduct ("free product") of the RX as R0-rings. An easy way to obtain an R-module M is to choose for each X E A U {0} an Rx-module Mx, and put M = MA OR; R. Such an M will be called a "standard" R-module. (Note that these include the free R-modules.) We obtain results on the structure of standard R-modules and homomorphisms between them, and hence on the homological properties of R. In particular: (1) Every submodule of a standard module is isomorphic to a standard