Mice count morally because they can be harmed. This raises a moral issue in animal experimen- tation. Three main ethical attitudes towards animals are reviewed here. The Kantian view denies moral value to animals because they lack reason. The second view, by Singer, considers animals as sentient creatures (i.e., able to suffer). Finally, Regan considers that animals are subjects of their own life; they are autonomous and therefore have moral rights. Singer is a reformist and allows animal experimentation under certain conditions. Regan is abolitionist, saying that animals have moral rights that cannot be negotiated. Current animal protection legislation strives to put in balance the human and animal interests to decide whether an animal experiment is morally justified or not. An ethical evaluation process is conducted based on the harm-benefit assessment of the experiment. The researcher has to implement the 3Rs (Replacement, Reduction, Refine- ment) to minimize the harms to the animals and make sure that the outcomes are scientifically significant and that the quality of the science is high, in order to maximize benefits to humans and animals