How do states design dispute settlement mechanisms in preferential trade agreements? And why do they choose the design features they eventually decide upon? This study proposes to test established theories of institutional design with a new dataset, and explores the possibility of an alternative explanation: institutionalist theory considers acts of design to be unique and idiosyncratic acts. Yet, instances of institutional design may be related to other, previous instances of institutional design. Drawing on diffusion theory, this paper proposes a new set of hypotheses which allows to address the interrelatedness among individual acts of institutional design.