The trend towards organic wine is recognisable in the growth of the organic vineyard area in all regions of Europe and the growing success of this type of wine in contests and tastings. Spain currently has the largest area of organic vineyards in the world. The aim of this research in progress is to study the transition to organic production in the region of Castile and Leon (Spain). Under the institutional framework of the DOs (Designations of Origin), a clear shift towards quality production was effected in the last forty years. Its position with regard to sustainability, specifically towards organic wine, has not been sufficiently researched yet. Despite having certain comparative advantages over other regions, such as its climatic and soil situation, the number of wineries engaged in this change is growing relatively slowly. On the other hand, factors such as the high level of bureaucracy involved in adopting certain sustainability initiatives have a negative effect. In the light of the theoretical framework provided by the theory of conventions, we study which justifications DOs and winemakers use in order to reach sustainable agreements, and which ones lead them to opt (or not) for the transition to organic production.