Animal welfare has become the key concept in EU animal protection law and is often used as a slogan in political speeches. It is a complex concept, however, that is often misunderstood. Its politico-scientific origins leave their mark, blurring its ethical purpose. Its implementation is as promising as it is chaotic, as shown by the example of cage farming. A case study of the European Citizens’ Initiative (ECI) “End the Cage Age” shows that the ethical purpose is both served and undermined by the necessary mobilization of scientific data.