KEYS for the identification of specimens have been used by biologists for several centuries. A method is described here for generating such keys automatically by computer, instead of composing them by hand, which until recently was the only way to produce them. The use of keys is not confined to biology, and applications for the computer method have been found in the earth sciences, medicine and engineering. Fig. 1 is an example of a computer-produced key for the British species of plants of the genus Epilobium L. (Willow-herb). It should be emphasized that the key-generating program is primarily a tool for the identification of objects and not for their classification, although it is in fact capable of creating a crude classification for the purposes of constructing a key.