In this paper we address the attempt to develop a common European standard for animal welfare. We examine this process as an intervention to simply the plethora of claims now made about farm animal welfare through labels and brands that order farming practices in particular ways by defining new goals, values, and competences through diverse forms of organisation. The paper is based on recent research from Welfare Quality® (www.welfarequality.net), an EU funded project that set out to accommodate societal concerns and market demands, develop reliable on-farm monitoring systems, product information systems, and practical species-specific strategies to improve farm animal welfare. The paper presents evidence from one aspect of the project, the welfare monitor of broiler chickens, which was evaluated through a series of interviews with free range chicken farmers in the United Kingdom. The paper does three things. It explores how farmers define what they do to improve the welfare of chickens; what they do to assess what they do; and what they think of the of the Welfare Quality assessment. In so doing it highlights the competing knowledge claims of farmers and animal scientists and draws out some implications for: 1) our understandings of free range farming, and: 2) controversies between different forms of expertise. From an STS perspective, we address the question of how much flexibility and attention to specific conditions can be built into a common animal welfare standard in order to make it a fluid technology that can work in different locations to address the diversity and multiple definitions of farm animal welfare now evident in the European farming industry.