The Sykes–Picot agreement embodies a certain style of diplomacy: an assumption of European predominance, given expression through cartographic line-drawing, terms of art (“protection,” “independence,” “interests”), and a structural secrecy which kept agreements from rival European powers, on the one hand, and from the peoples most affected, on the other. It is this element of secrecy that constitutes the focus of the present contribution. I situate the Sykes–Picot agreement in a prewar pattern of secrecy as diplomatic technique, explore its role in spurring a new regime of publicity for treaties, and take it as a touchstone for exploring whether this new regime could achieve a fundamental transformation of prevailing modes of diplomacy.