A veterinarian with specific professional or scientific interest in toxicology should be aware of the alternative methods in toxicology testing, advise on replacement and refinement of laboratory animals used in toxicological studies and safeguard animal welfare. The main aims of this chapter are to outline the major aspects of in vivo and in vitro models in toxicity testing and to give a brief overview of endpoint determination. The principle focus will be to highlight some of the current in vivo and in vitro models available in toxicity testing and inform on new technologies and approaches used in this field. In vivo models in toxicity testing