Chapter 65 Farm Size What patterns can be discerned in the distribution of farm sizes across countries and over time How does the behavior of individual economic agents interact with the natural environment and general economic development to affect farm size How has concerted human intervention understood as national and supranational policy actions altered these outcomes We find that operated farm size rises with economic development especially in the 20 th century with marked exceptions: large farms in Latin America and Southern Africa; small farms in parts of Northwest Europe; diminishing farm size in South Asia. Despite increased scale in many advanced countries the family remains the main source of farm labor. Hired labor supervision costs tend to favor family farming as the equilibrium institution. Theory suggests that the family farm will typically become larger with economic development but its efficiency advantage over the agroindustrial enterprise will decline. Sufficiently land augmenting technical advances can upset the relationship between development and equilibrium scale as in the Green Revolution. Concerted intervention can also cause departures from such equilibria. Colonial land grabs have led to inefficiently large farms with market forces and land reform subsequently reducing average size after decolonization. Greater land rights have thereby raised the rural poors income status and power but farmland collectivizations and much farm tenancy reform have largely failed to achieve this goal. However classic land reforms and some decollectivizations have proved more incentive compatible and have distributed large land areas among many small family managed units. Farm size is in principle also affected by net taxes on farm production (mostly negative in OECD mostly positive in developing countries though reduced) but such effects remain empirically elusive. Globalization and liberalizationeffects via relative prices asidehave induced institutional changes that are not neutral with respect to farm size. These include supermarkets increased role in the supply chain.