The use of animals in cancer research continues to be important for the study of tumor biology, the development and testing of new therapies, and risk assessment. The new knowledge generated from this research contributes to the health and welfare not only of human beings, but also of animals which develop cancer. However, the use of animals for cancer research is a privilege which carries with it scientific, professional, and moral obligations. The three tenets of a sound animal research program include good science, humane care, and regulatory compliance. Recognizing the complex interactions in the tumor-animal model, the investigator needs to address a wide range of issues during experimental design and implementation including animal welfare concerns, complicating factors in colony management, and compliance with laws, regulations, and policies. Therefore, both practical and philosophical considerations enjoin researchers to maintain the highest standards of animal care.