The relationship between ethics, science, law and animal welfare is a complex but necessary one. Ethical decision-making addresses the question: ‘Should we do something?’. When this question relates to sentient animals, the answer is informed in a utilitarian analysis by what we know about the likely animal welfare benefits and harms of undertaking an action or not. That information is gleaned from animal welfare and behavioural science, often through research which itself requires ethical approval to be legal . Even in a non-research setting, national and international legislation additionally constrains our ethical decision making. Generally, an action which is considered ethical because it optimises animal welfare will be legal, and an action which unnecessarily compromises animal welfare (and would therefore be unethical) is illegal. Sometimes, however, possible actions are identified which may be strictly illegal but nonetheless benefit animal welfare: an ethical challenge which may reveal conflicts between personal and professional morality. This presentation uses case examples to discuss how basing ethical decision making in three ‘central tenets’ can aid the consistent development and application of regulation and legislation across disciplines and species. It will demonstrate how ethicists, scientists, veterinarians, lawyers and regulators share responsibility for optimising animal welfare across research, clinical and judicial settings; elucidate the challenges which working in this necessary cross-disciplinary space can present; and suggest possible ways of resolving them to the benefit of the animals whose best interests we all wish to safeguard.