Climate change models can be improved by incorporating past human landscape transformations. Accurate maps of global agricultural history are critical in this regard. Agriculture is one of the oldest, most thorough, and spatially extensive of all human activities on Earth. This symposium provides the results of a 4-year project by geographers, archeologists, historians, and economists from the United States and Sweden. Global and continental scale maps are presented for AD 1000, AD 1500, and AD 1800 with discussion of 19th and 20th century agricultural developments. Changes during the past millennium occurred suddenly, in great leaps, not in a slow and continuous manner. Qualitative changes within existing agricultural systems -- intensification -- were as important as quantitative changes -- expansion -- of previously established patterns of land use.