The protection of farm animal welfare is a society issue. It stems from the recognition that animals under our care are sentient beings. Recent scientific data on mammals, birds, and fish provide evidence that these animals can feel emotions. Indicators of animal well being, assessing their emotional status or the impact of farming conditions, are now available. Solutions are found to balance welfare and production requirements. However, science alone cannot fully address the issue of animal welfare, as it cannot define the limits of what is acceptable and what is not. Nevertheless, science must provide arguments for a constructive debate, such as indicators of welfare and of the impact of farming conditions. It can also help understand ethical reasoning, and include this data in welfare evaluation systems.