Animal research has been controversial since its inception. Proponents cite the ethical obligation to contribute to medical and scientific progress with the knowledge gained from animal testing. Critics of animal testing argue that animals have morally relevant claims that outweigh considerations in trade-off situations. Furthermore, the transferability of animal models to humans is questioned. Legislators attempt to resolve conflicts between research freedom and animal welfare by requiring an ethical assessment between scientific knowledge gain and the burden on the test animal as a prerequisite for the approval of an animal experiment. Although the search for alternatives to animal testing has now become an important research focus across Europe, the number of animals used in experiments remains significant.