The significance of ambiguity – Evidence-based practice in social service with children and youthEvidence-based practice (EBP) has gained a central position as a model of knowledge for social work in the public sector. In the Swedish Government Report about knowledge-based social work from 2008, EBP is described as a useful way of structuring the social services on a scientific basis (SOU 2008:18). Following on this, and in order to establish EBP in social work practice, between 2009 and 2016, there were annual agreements between the government and the Swedish Association of Local Authorities and Regions (SALAR). As defined by the annual agreements, a national network of Regional Development Leaders (regionala utvecklingsledare) was given the task of producing regional plans of action for the establishment of EBP in the municipalities. The article examines how the Regional Development Leaders in the so-called Children and Youth Investment (Barn- och ungasatsningen) interpret and implement EBP as a model in public social work. The study is based on interviews with 22 out of the 37 Regional Development Leaders that were part of the Children and Youth Investment in 2016. Ernesto Laclau’s theory of empty signifier serves as an analytical tool. The analysis shows that the ambiguity surrounding EBP creates discretion for the Regional Development Leaders. This discretion allows them to use EBP as a ”signifier without a signified”; a model that they can fill with different meanings depending on purpose and context. In that perspective, EBP appears as a floating term and can be characterized as an empty signifier. One of the main results stresses the fact that the Regional Development Leaders describe EBP as a model of governance rather than a model of knowledge. Despite its ambiguity, EBP fills a significant function for the development of knowledge-based social work practices in the public sector.