Models of production and inventory systems are frequently employed in the design and performance studies of manufacturing systems. Despite their potential applicability, their use is not widespread. This is mainly due to the absence of comprehensive tools for analyzing manufacturing systems. The proposed research aims at rectifying this situation by carrying out the following three tasks: 1) Devise exact and approximate procedures for analyzing networks of production/inventory systems with finite work-in-process inventories. 2) Develop exact algorithms to study single-stage, multi-item production/inventory systems with (R,r) inventory control policies and switch-over rules. 3) Incorporate the algorithms developed in Part 2 into the approximation algorithms of Part 1 to be able to study multi-stage, multi-item projection/ inventory systems.