Amb. Peter Jenkins, twice British Ambassador in the UK Mission to the International Atomic Energy Agency, from 2001 to 2006, and a current member of the British Pugwash Executive Committee, has had extensive experience of negotiations on Iran’s nuclear programme. Following the Joint Comprehensive Plan of Action (JCPOA), agreed in July 2015 between Iran, the P5+1 and the EU, he outlines the lessons that can be learned from the difficult and prolonged process of negotiation. This article was first published in the RUSI Newsbrief (vol. 36:2) in March 2016.