The modern digger derrick is a complex machine which can perform numerous operations. A variety of machines are available and the user must match his requirements to the products offered if he is to procure the most efficient one. The primary variables that are reviewed in detail are configuration, capacity, digging requirements, and stability. Controls and accessories are briefly reviewed. Two work sheets are presented. The first provides assistance in determining the configuration best suited for the user's needs and, the second serves as a check list to assure that the final specification has not omitted necessary information.