This article explores the part played by Sir Henry Dobbs, the ‘man on the spot’, in shaping the 1921 Anglo-Afghan Treaty. The treaty provisions being negotiated were important to the security of the Indian frontier, internally and internationally, as they defined the formal relationship between India and Afghanistan right through until Indian independence. In contrast with existing accounts, the analysis presented here contends that Dobbs did have a significant influence both on the negotiating process and on the eventual result. It demonstrates how in his role as chief negotiator Dobbs drew on experience and techniques that he had earlier acquired as a political officer in frontier areas. His aim seems to have been to influence matters so that the treaty would deliver on what he regarded as important while giving away nothing that he thought damaging. The article thus sheds light on how—in a novel and volatile context—Dobbs handled differing views in London and Delhi, and negotiated with the Amir. Given the necessary authority by the British Government, he finally arrived at an agreement accepted by the various parties—Afghans, the Viceroy and the British Government in London. The source for this revised perspective on the negotiations and fuller understanding of his role are Dobbs’ recently-discovered letters and private papers, previously unavailable to historians, together with a re-examination of official sources prompted by this new material.