Consisting of four scientific papers and a comprehensive overview, this thesis concerns governance in and of social work. More specifically, it studies governing of knowledge in social service with children and youth. Through the growing focus on evidence-based social work since 2000, state governing of knowledge has become an increasingly established concept. In general terms, it refers to the national level’s efforts to govern based on knowledge in order to solve social services’ ”knowledge problems”. However, there are more aspects to state governing of knowledge. Thus, this thesis focuses on the doing of such governance – a praxis that involves actors at national, regional and municipal levels. Here, regional development leaders in social service with children and youth are one of the central actors; consequently, they constitute the empirical focus of the thesis when analysing the doing of governing of knowledge. The aim of this study is to describe and analyse how state governing of knowledge is conducted by examining how development leaders perceive and concretise the task of governing of knowledge in social service’s childcare. The overall questions are as follows: 1. How do regional development leaders in social service with children and youth perceive and interpret the EBP knowledge model in relation to their task? 2. How do regional development leaders act when they govern with knowledge within social service? 3. What characterizes the professional practice of regional development leaders, and how can we understand it in the context of governance? Data have been collected through individual interviews and focus group interviews with 28 regional development leaders. In addition, the empirical material includes a field study with participant observations during network meetings and a questionnaire survey with 29 development leaders. The data have been analysed from three theoretical perspectives: governance as floating signifier, governance as joint doing, and governance as a relational exercise of power. The first perspective, governance as floating signifier, implies that governance changes over time, both in terms of how it can be understood and how it is applied. The second perspective, governance as joint doing, refers to governance as it takes place in and through interaction between actors involved in governance. Here, we can note a mutual influence between those who govern and those who are being governed. The third perspective focuses on power as a central element of governance and how it is constructed in a relational interaction between actors who are part of a common context of governance. The analysis shows that the ambiguity that surrounds state governing of knowledge creates a discretion for interpretation and action. This gives development leaders the opportunity to saturate their work with their own content, depending on the purpose and context, which is very much about developing and organising social work in social services. Working with development, change and innovation is thus of importance in the governing of knowledge of social service with children and youth. In carrying out their tasks, development leaders combine hierarchical top-down management with horizontal, relational management. This becomes evident in the development leaders’ choice of governance practices, which involves networking with managers in senior positions who have a mandate to make decisions. The interaction between development leaders and managers is characterised by mutual influence, which results in development leaders sacrificing certain areas of their mission in favour of activities that managers consider important to implement. Such governance praxis is likely to have implications for the outcomes of governing of knowledge. The establishment of the development leader as an actor in the governing of social work can be understood as a reaction to changing institutional conditions for the management and organisation of the public sector. The work of development leaders is characterised by a hybridised professional practice: they integrate seemingly incompatible logics and thus have to manage different tensions in a professional role, which is probably a prerequisite for navigating complex governing tasks.