The Southeastern Anatolia Project (Güneydoğu Anadolu Projesi, GAP) is arguably the largest regional development project ever witnessed in Turkey. Begun in the 1970s, GAP initially aimed primarily at the construction of 22 dams and 19 hydroelectric power plants on the Tigris and Euphrates rivers and of extensive irrigation networks to produce hydroelectric energy and water 1.8 million hectares of land in southeastern Turkey. Later, the scope of GAP broadened significantly as it became a more ambitious and comprehensive scheme of modernization and transformation. Following this expansion, the multidimensionality of GAP and its multifaceted implications became clearer at both the national and international level. The project grew more visible and influential not only in political and public discourses, but also in the GAP region itself. Despite these developments, however, the question of how the project’s characteristics, vocabulary, rationales, and mechanisms have changed since its inception remains underdiscussed. This article asks what GAP was in the past and what it has more recently become. It examines the gradual transformation of GAP over forty years by specifically taking into account the continuities and ruptures in development discourse, theory, and practice since the 1950s. In this way, the article aims to provide a new perspective regarding the stages through which the project has passed to reach its current form.