The paper analyses the role of third country lobbying in the EU. The novelty of the paper lies in applying insights about lobbying to the implementation and enforcement stages, not only, as is traditionally done, to the legislative stage. The contribution focuses on the lobbying efforts of the US, China and Japan in the context of EU chemicals law- and policy-making. The empirical research material consists of in-depth interviews with third country lobbyists and EU policy-makers. The findings illustrate that third countries play diverse roles in REACH regulation throughout the policy cycle. The paper emphasises the ability of third country lobbyists to provide feedback to the EU legislator especially at the later stages of policy-making to the extent that, intentionally or not, they function as ancillary legislators. Third countries enter the policymaking process “in through the back door”, as there is limited public oversight of activities at the implementation and enforcement stages. The contribution concludes by examining the ways in which to increase transparency about third country activities.