In Switzerland, the decrease in the number of farms is widely seen as the dominant reason for land abandonment and forest expansion in the Alps. Also agricultural policy, which aims to preserve open land and to ensure cultivation of marginal lands, relies on this conclusion. However, based on production and location theory, contemporary concepts of agricultural economics and empirical indications, we suggest that the relationships between forest expansion and structural change in agriculture are more complex. In 2002, we have started a three year interdisciplinary project (agricultural econonnics, vegetation dynamics, geoinformatics and spatial modeling) that examines the following general research question: How can we explain the pattern of land abandonment and forest expansion in the Swiss Alps during the last decades with the help of newly available large quantitative datasets? Our target is to determine the relevant bio-physical and socioeconomic causes of land abandonment and forest expansion and to quantify their relative impact. We expect the findings to be significant for the understanding of land-use changes in the Swiss Alps; they may have important implications for policy design. In this contribution we review the state of knowledge on the processes of land abandonment and forest expansion in the Swiss Alps. On the basis of economic theory and vegetation dynamics we derive hypotheses and discuss the two methodical approaches planned: 1) a total area approach where large datasets on forest expansion are investigated with multivariate statistics and 2) an approach with time series of aerial photographs in selected case study areas.