Aristotle's has been the most influential philosophy in the whole history of science. Monte Johnson examines its most controversial aspect: Aristotle's emphasis on the importance of goals and purposes to scientific understanding--his teleology. In some cases this policy has proved deeply flawed, for example in his earth-centric cosmology, or his anthropology purporting to justify slavery and male domination. But in many areas Aristotle's teleology has been successful, and remains influential, for example in adaptationist evolutionary theory, embryology, and genetics. Johnson's book shows also how Aristotle's theory has profound implications for environmental ethics and for the theory of value in general.