We analyze trends in crop yields and yield variability of barley, maize, oats, rye, triticale and wheat in Switzerland from 1961 to 2006. It shows that there have been linear increases in crop yields since the 1960s. However, yields of barley, oats, rye, triticale and wheat have leveled off in Switzerland since the early 1990s, which contrasts linear trends in cereal yields that is usually assumed for Europe. We show a relationship between the introduction of agricultural policy measures towards environmentally friendly cereal production that fostered widespread adoption of extensive farming practices and the observed leveling-off of crop yields. Thus, this paper emphasizes that agricultural policy can be an important reason for slowing crop yield growth. Agricultural policy measures will be one of the key driving forces of future crop yields. Thus, the potential leveling-off of crop yields that is indicated in this study should be considered in analyses of future land use and food supply as well as in the evaluation of agri-environmental measures and policy reforms.