Good animal welfare is linked to the quality of research data derived from laboratory animals, their validity as models of human disease, the number of animals required to reach statistical significance and the reproducibility of in vivo studies. Identifying new ways of understanding and improving animal welfare, and promoting these in the scientific community, is therefore a key part of the work of the National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). Our strategy for animal welfare includes funding research to generate an evidence base to support refinements, office-led data sharing to challenge existing practices, events and networks to raise awareness of the evidence base, and the creation of online and other resources to support practical implementation of refinement opportunities.