Acknowledging the existence of internally displaced persons (IDPs) and responding to it represent a challenge to state sovereignty. However, an increasing number of state policies specifically address IDPs. Moreover, many differences and even contradictions arise from state responses to internal displacement. This thesis identifies and accounts for the various ways in which states engage with the IDP protection norm through national public policies. Using a constructivist approach, it conceptualises the institutionalisation of the IDP protection norm at the domestic level, analyses it, and explores what it implies for the exercise of state sovereignty. The thesis proposes and assesses three dimensions of institutionalisation – the scope, the level of formalisation, and the level of internalisation – to show variation across all relevant cases of state engagement with the IDP protection norm, based on an original data set. It accounts for such variation by exploring the influence of three main motives (human rights, economy, and security) on decisions taken by state officials —each motive being associated with a set of actors and conditioned by two elements, the state’s normative framework and the political system. To test this framework, this thesis compares three cases, using in-depth process tracing, mainly based on fieldwork data: Colombia (1995-2016), Peru (1993-2016), and Kenya (2007-2017). The case studies confirm the relevance of the three motives in accounting for variation, highlighting the importance of both the interaction between and the relative importance of each motive in shaping states’ engagement with the IDP protection norm. Finally, this thesis interprets state engagement with the IDP protection norm as a reaffirmation of state sovereignty, by unpacking the constitutive rule into four components: responsibility, control, recognition, and autonomy. The three case studies suggest that states simultaneously exercise different components of sovereignty, and that this interplay is central to understanding variation in states’ engagement with the IDP protection norm.