The first section focuses on the development and validation of welfare indicators generally, in terms of their relevance to animal well-being, their inter-observer reliability, and the confidence with which the prevalence of described features can be estimated. Challenges in this work include accounting for the ways in which welfare measures may fluctuate over time, and identifying measures suited to monitoring positive welfare states. The second section focuses more specifically on qualitative welfare indicators, which assess the ‘whole animal’ and describe the expressive qualities of its demeanour (e.g. anxious, content). Such indicators must be validated in the same way as other health and behaviour indicators, with the added challenge of finding appropriate methods of measurement. The potential contribution of qualitative indicators, however, is to disclose an emotional richness in animals that helps to interpret information provided by other indicators, thus enhancing the validity of welfare assessment protocols. In conclusion, the paper emphasises the importance of integrating such different perspectives, showing that new knowledge of animals and new ways of relating to animals are both needed for the successful development of practical welfare assessment tools.