International audience ; Based on extensive empirical fieldworks conducted in Belgian and French family justice courtrooms in order to explain how culture and ethnicity are processed and understood in the daily reasoning and assumptions of legal professionals, this chapter analyzes different forms in which culture and ethnicity are framed in family law cases. Understanding how and along which dimensions these elements do vary in judicial reasoning constitutes the preliminary but necessary step before assessing the need of cultural expertise as such. In this attempt, we shed light on a scope of variations between complex and non-deterministic models of culture-consistent with contemporary anthropology literature-and more simplistic ones, in which culture and identity are conceived as fixed realities. Throughout this path between norms, facts and stereotypes, we illustrate not only the multiplicity and complexity of forms which cultural elements can take in the exercise of family justice, but also the risks that some significances may carry with them and the urgent need to improve more fluid and dispassionate conceptions of cultural diversity before developing "cultural expertise" as such, an expertise that could otherwise reinforce stereotypical and fixed views of "cultures".