This is the final unit in a six-unit series on the design, purchase and implementation of a GIS. This unit focuses on the benefit/cost analysis: what it is, why it is useful and how to approach it. It discusses how costs, both one-time and recurring, may be determined and how benefits of a GIS may be quantified or otherwise identified. A method for comparing costs and benefits is outlined and illustrated through an example from the Department of Natural Resources, State of Washington.