In 2013, the G-20 asked the OECD to develop new rules for corporate tax transparency, pushed by civil society activists. World leaders had agreed that increased transparency was urgently needed to help shore up national fiscal systems and alleviate social injustices. These new rules have wide-ranging economic and political consequences for the regulation of global wealth chains (GWCs). Tax transparency is a key factor in the level of information asymmetry between wealth chain ‘insiders’, such as corporations and tax advisers, and ‘outsiders’, such as tax authorities and civil society activists. This chapter discusses the ‘technicisation’ of the OECD policy process to define these new requirements, i.e. the embedding of highly political discussions in a specialised, expertise-intensive policy context. Technicisation constrained the post-crisis political momentum for expanded transparency of corporate wealth chains, but also helped normalize the idea of increased transparency as ‘risk assessment’ within the policy community. The chapter highlights three key dynamics of technicisation: policy insulation, re-framing and appropriateness judgments. Evidence is drawn from a qualitative content analysis of documents in the OECD policy debates on corporate tax transparency, and interviews with select informants involved in the policy process.