Toxicology has made tremendous strides in the sophistication of the models used to identify and understand the mechanisms of agents that can harm or kill humand and other higher organisms. Non-animals or in vitro models started to gain significant use in the 1960s. As a result of the increased concern over animal welfare, economic factors, and the need for greater sensitivity and understanding of mechanisms, interest in in vitro^n models has risen. This volume demonstrates that there now exists a broad range of in vitro models for use in either identifying or understanding most forms of toxicity. The availability of in vitro models spans both the full range of endpoints (irritation, sensitization, lethality, mutagenicity, and devlopmental toxicity) and the full spectrum of target organ systems (skin, eye, heart, liver, kidney, nervous system, etc.). Chapters are devoted to each of these speciality areas from a perspective of presenting the principal models and their uses and limitations. Chapters that overview the principles involved in the general selection and use of models, and that address the issues of safety concerns and regulatory acceptance of these methods are also included.