Laboratory mice are the world's most widely used research animal - environmental enrichment is now standard but quality and implementation vary significantly.
Laboratory mouse welfare has improved substantially since the 1990s as enrichment evidence accumulated and regulatory requirements strengthened. However, implementation is inconsistent across facilities and research groups. The scientific case for enrichment is reinforced by evidence that enriched mice produce more reproducible and translatable research results - reducing enrichment to 'simplify' experimental conditions undermines both welfare and science. Nesting material is the single most important enrichment for mice and should be considered a minimum welfare requirement. Facility-wide enrichment programmes with standardised implementation produce the most consistent welfare and scientific outcomes.