This thesis aims to understand how the Open Method of Co-ordination (OMC) has developed at the European level and to explore how, and with what effect, it has influenced the EU Member States. My cases are policy areas, which have been selected on the basis of their salience in Member States. The case of high salience is employment policy and the case of low salience is anti-poverty policy. Regarding the European level, the thesis seeks to identify the main causal factors that determine the development of the OMC. I use an adapted version of the Principal-Agent framework, where the Member States represent the Principal(s) and the European Commission represents the Agent. While most existing literature analyses the OMC at one moment in time, I analyse how the OMC develops through time, where I distinguish between emergence, when it has not been fully established, and evolution, when it has been fully established as a policy coordination instrument. I develop two hypotheses to test Commission-Member State interaction during OMC development during emergence and evolution and two to test if their interaction differs in cases of high and low saliency. My findings show that the Commission has a greater influence during the emergence of the OMC and that the Member States have more influence during the evolution of the OMC. The saliency of a policy issue only minimally influences Member State and Commission interaction in the two cases. For the national level, the thesis seeks to shed some light on how and the extent to which the OMC has been integrated into the domestic contexts of (14) EU Member States. The endeavour is first to draw some general conclusions about how governmental and non-governmental actors in Member States use the OMC. My findings show that it has mainly been used as a policy reporting instrument, but has in some cases also been used for policy development. The aim is secondly to assess the extent to which the general objectives of the OMC have been achieved. My findings show that it does not define core reform programmes in Member States, which is hardly surprising, since the OMC is a soft policy instrument.