In the past 200 years, moral theories and attitudes toward both humans and animals have changed considerably. These changes have led to widespread criticism of animal use in some or all research and testing. For the most part, the debate has been marked more by rhetoric than scholarship, but the underlying philosophical theories and their protagonists have been a very important influence on the modern debate over animal use. This paper examines some of the moral philosophy and attempts to present the main arguments concisely and simply and to refute common misconceptions.