Animal welfare is a state within the animal. Scientists use 2 main conceptual frameworks for understanding animal welfare: biological functioning and affective state. These 2 frameworks were initially seen as competing, but more recently biological functioning is recognized to include affective experiences and affective experiences are recognized as products of biological functioning. While science provides us with the ability to understand how the body responds to physical challenges and affective states, our ability to monitor some affective states is under-developed. Thus most studies have used the biological functioning framework to infer compromised animal welfare, on the basis that suboptimal biological functioning accompanies negative affective states. There is increasing societal interest in providing domesticated animals with the opportunity for positive affective experiences and this will also be a major focus for animal welfare science in the early 21st century. Furthermore, animal welfare science will continue to identify conditions and strategies to prevent and ameliorate negative states in farm animals, and extend the range of animal welfare indicators for use on-farm in risk assessment and management, welfare benchmarking and welfare auditing. Science thus should provide the facts, but what society, groups or individuals do with these facts is a philosophical decision. Exclusion of science can result in emotive or self-interested arguments from sectional groups dominating community debate. This is not to say that such arguments should be ruled out; quite the reverse, as they reflect, in part, current community values. However, they should contribute to, not pre-empt, the debate. Furthermore, these ethical questions should include other considerations, such as our duties toward animals and human health, economic, social and environmental consequences. Thus, in resolving the question of whether or not a particular animal use is acceptable, science provides the means to understand the impact of each animal use on the animal and has a prominent role in underpinning decisions on animal use and the attendant conditions and compromises.