This article elaborates the notion of ‘nuclear idiosyncrasy’ as a specific understanding of what nuclear weapons and energy are, what they stand for and what they can do. It then assesses the persistence of nuclear idiosyncrasy over time and its effects on French nuclear policies in the United Arab Emirates (UAE) and Iran. Based on interviews in France, Geneva and the UAE, this article contributes to three debates within foreign policy analysis and nuclear history. Is a regional approach necessary to understand the framing of foreign policies in the twenty-first century? Does a change in leadership fundamentally affect the orientations of nuclear policies? Are the risks of nuclear proliferation in the Middle East and the measures to prevent it similarly understood by all the players in the international community? First, it shows that French nuclear policies in the Middle East are not shaped by dynamics specific to the region as the often invoked notion of an ‘Arab policy of France’ would suggest. Secondly, in-depth analysis leads one to reject the idea of a major change between the nuclear policies of Presidents Chirac and Sarkozy. Thirdly, persistent French nuclear idiosyncrasy leads also to rejection of the idea of convergence towards a shared understanding of the proliferation threat in the Middle East.