Abstract: During the last decades, EU integration processes and their governance have become more complex, adding to the classic hard law method (i.e. regulations, directives) other based on non-binding instruments (the most exemplary one being the Open Method of Coordination). This paper addresses a basic puzzle concerning the later, and more specifically that of voluntary compliance: Why do national actors voluntarily implement EU measures in nationally sensitive policy domains (such as research and higher education) that could change existing (institutionalised) procedures, rules and practices? Our interest is to examine which factors account for voluntary compliance. Here we draw upon the literature on compliance, paying attention to four main explanatory arguments, all of them assigning a key (though different) role to institutions: ‘goodness-of-fit’ (institutional similarity between organizational arrangements and policies and rules to comply with), enforcement (rules also provide sanctions/rewards), management (organizational rules and capacities facilitate compliance), and normative commitment (compliance occurs because it is what it should be done). Besides, we elaborate on these explanatory arguments, focusing on the mechanisms connecting the institutional level to the action level. Here, we resort to March and Olsen’s (1984) well known duality between ‘logic of expected consequences’ and ‘logic of appropriateness’, showing how the pairing of both logics could reinforce each other and eventually increase the likelihood of complying. To test these arguments, we use the case study of the implementation in two different countries (Norway and Spain) of a central pillar in the building of the European Research Area (ERA) regarding human resources and mobility, the European Charter for Researchers and Code of Conduct for the Recruitment of Researchers.