In a highly original and provocative essay entitled “Behavior, Purpose and Teleology”, published a few years ago, Professors Arturo Rosenblueth, Norbert Wiener and Julian Bigelow attempt to indicate the scientific importance and usefulness of the concepts of purpose and teleology. Since this essay appeared the suggestions it contains seem to have acquired a significance which was not wholly apparent at that time. This is due primarily to the fact that a somewhat novel and, it appears to some, revolutionary approach to certain problems has arisen in the sciences, an approach which is more or less loosely referred to as “cybernetics,” and among whose outstanding spokesmen are to be found the very authors of this essay—particularly Professor Wiener, whose recently published Cybernetics has been claiming the attention of an increasing number of scientists and non-scientists alike. In his book, it may be noted, Professor Wiener, in tracing the development of cybernetics over the past few years, gives a good indication of the importance he attaches to the earlier essay. He writes, with reference to it: “The three of us [Rosenblueth, Wiener and Bigelow] felt that this new point of view merited a paper, which we wrote up and published. Dr. Rosenblueth and I foresaw that the paper could only be a statement of program for a large body of experimental work, and we decided that if we could ever bring our plan for an interscientific institute to fruition, this topic would furnish an almost ideal center for our activity” (p. 15). It would seem, then, that an examination of the contents of this essay should not be without interest at this time.