Radiotherapy can be delivered with different types of machine, such as external beam high energy radiation machines, kilovoltage machines and brachytherapy equipment. Variation in the incidence of different cancer types, the complexity and cost of treatment technologies, and differences in local social, economic and physical circumstances are all factors that influence technology acquisition, purchase and implementation. This publication addresses one of the many factors, associated with the planning of a new radiotherapy facility or the upgrade of an existing one - the selection of a high energy (megavoltage) radiotherapy machine. The two main high energy machine types are medical linear accelerators (linacs) and cobalt?60 machines. Although both treatment modalities have been compared extensively in the relevant literature, very few publications describe all the issues to consider when choosing a megavoltage machine. This publication puts all appropriate questions into context and provides information for non?technical administrators and decision makers, and for professionals directly involved in treating patients.