Public and consumer pressure for assurances that farm animals are raised humanely has led to a range of private and public animal welfare standards, and for methods to assess compliance with these standards. The standards usually claim to be science-based but while research has developed measures of animal welfare and tested the effect of housing and management variables on welfare within controlled laboratory settings, there are challenges in extending this research to develop on-site animal welfare standards. The standards need to be validated against a definition of welfare that has broad support and which is amenable to scientific investigation. Ensuring that such standards acknowledge scientific uncertainty is also challenging, and balanced input from all scientific disciplines dealing with animal welfare is needed. Agencies providing animal welfare audit services need to integrate these scientific standards and legal requirements into successful programs that effectively measure and objectively report compliance. On-farm assessment of animal welfare requires a combination of animal-based measures to assess the actual state of welfare with resource-based measures to identify risk factors. We illustrate this by referring to a method of assessing welfare in broiler flocks. Compliance with animal welfare standards requires buy-in from all stakeholders and this will be best achieved by a process of inclusion in the development of pragmatic assessment methods and the development of audit programs verifying the conditions and continuous improvement of farm animal welfare.