Farm animal welfare has now been studied, within a scientific framework, for several decades. The framework does not include ethical issues, but unless measurements of animal welfare at farm level are embedded in an ethical context, there is a danger that these measurements will not be properly utilised. This paper considers the relationship between ethical questions and animal welfare assessment. In it, the following four key ethical questions are identified. What is the baseline standard for morally acceptable animal welfare? What is a good animal life? What farming purposes are legitimate? What kinds of compromise are acceptable in a less-than-perfect world? The authors suggest that animal welfare scientists need to reflect carefully on these questions if welfare assessments are to be properly interpreted and put to practical use. Such reflection will lead to a more transparent appreciation of the values underlying welfare assessment. In this way, it will both offer welfare scientists a greater awareness of their own value-assumptions and enable the same scientists to communicate effectively with the wider audience — farmers, consumers, pressure groups, policy-makers and so on — for which the results of animal welfare assessments are of concern.