In the Mekong Region, the Asian Development Bank and partners have promoted economic corridors as a way to achieve regional economic integration and growth. This study evaluates how a transboundary policy narrative of shared prosperity around the East-West Economic Corridor programme emerged, and then how it was elaborated and used, taking a set of border policies of the government of Thailand as cases. For two decades the shared prosperity narrative has been used by a coalition of elite actors to support a programme of investments in road infrastructure, as well as to push for agreements on trade, border logistics, investment and tourism. The shared prosperity narrative has helped maintain support for the programme despite its failures to meet projections and expectations. Although criticised by civil society and experts from time to time, no coherent shared counter-narrative emerged. Policy elites in Thailand have used the transboundary narrative to justify investments in special economic zones, and transport infrastructure near the border and inside neighbouring countries. Thailand has also reproduced the narrative in support of efforts to bolster tourism cooperation, and negotiate cross-border trade and logistics agreements. Roads and bridges have been built, underlining how discursive practices have material consequences and reinforce the narrative.