The number of farms has decreased since the 1930s, and average size-measured in acres-has increased. Most farms are small, and more than half have sales less than $10,000. As a result, households operating small farms rely heavily on off-farm income from the local economy. At the other extreme, some farms have sales in the millions. These and other differences present challenges when analyzing the economic structure of agriculture and developing farm policy recommendations. USDA's Economic Research Service has developed a classification to address variations across farms, with an emphasis on small farms.