Following a brief outline of the characteristic features of the systems approach to training, the information-processing model is identified as a particularly illuminatina appoach to job classification. It is argued that the model highlights the multi-dimensional nature of task difficulty, indicates appropriate training methods, and provides a language for describing any human skill. The problem of deriving a meaningful classification of cognitive skills is discussed, and it is suggested that higher order mental processes can be broken down into four distinguishable stages, each with its own potential sources of difficulty. The implications of the systems approach for selection are then considered, and it is argued that there is a need. for increased flexibility and sophistication in diagnostic testing. Fiinally examples drawn fromi recent studies conducted within the Royal Air Force are adduced to illustrate the kinds of improvemnent in performance which can be achieved through the appllcation of a systemns approach to training.