Animal welfare science aims to objectively assess good or bad animal welfare in order to inform interventions, often focusing on win-wins that improve both human and animal lives. Based on scientific study many measures of welfare have been proposed, such as frequency of injury, ‘stress hormone’ (cortisol, corticosterone) levels in the blood, rates of negative behaviours like stereotypes (repeated, non-functional, often harmful behaviours) and conflict, or the occurrence of positive behaviours like foraging and grooming. These measures are used in a variety of ways: they inform new animal welfare laws; they feed into further scientific study; and they are used as indicators of good and bad welfare in assessment frameworks, for use in monitoring, comparison and marketing.