This report summarizes the findings and describes the products of a 2-part research project that examined the parameters of Washington's interlibrary loan cooperation statewide, and developed a set of computer models to be used in simulation studies of associated activities and policies. It contains a statement of the problem; an historical review; a description of methodology; a review of the findings of a statistical analysis conducted on interlibrary loan data; a discussion of the roles of an institution as a library and as a switching mechanism; explications and descriptions of the computer models and simulations; copies of the programs and portions of the printed output; and a bibliography listing 87 sources. It also provides a users' manual for the application of the models to simulate an institution's borrowing and lending activities for service planning and policy modification. (Author/FM)