The chapter deals with the semantic changes from a strictly market-oriented policy to ‘green and social procurement’ in European competition policy. It contributes empirically to the framing approach in the research on European politics by focusing on interest group framing. With an estimated share of expenditures of between 17 and 19 per cent of GDP in the EU, public procurement is of high economic relevance. In this policy subsystem we identify a shift from market-, state- and civil society-oriented policy frames to a de-politicised techno-juridical frame from the early 2000s onwards. Due to local discretion, party politics and European adjudication, the implementation of the Procurement Directive 2004 resulted in variegated rules at the sub-national level. Triggered by this divergence the frame of legal uncertainty has become the major impulse for re-regulation since 2010.