This article analyses why Green National Accounting based on the SEEA system and/or a “Green GDP” have not been seriously integrated in policy making processes, despite the long-standing public concern that economic growth may harm the environment. Combining a historical institutionalist and a public policy-oriented theoretical approach rooted in Political Science in order to understand this puzzle, we analyse the case of Denmark; a country widely seen as a green front-runner, and therefore a likely candidate for implementing Green National Accounting/a Green GDP in political-administrative decision-making. We identify several barriers that make a transition towards a Green GDP very difficult. However, with the change of government in 2019 a window of opportunity opened, and Denmark now seems to be on its way to introduce green economic models based on green national accounts, and eventually a Green GDP in policy-making; albeit incrementally and in a way that fits existing administrative procedures and existing economic models.