This paper analyses the evolution of agriculture’s participation in the US gross domestic product (GDP) from 1960 to 2001. An econometric model is run in order to identify the main variables that determine this participation. From 1960 to 2001, there is a downward trend of agriculture’s participation in the US GDP with a break from 1971 to 1973, in other words, agriculture’s participation in the US GDP decreased from 1960 to 1970, increased from 1971 to 1973 and decreased again from 1973 to 2001. The 1971-1973´s break in the downward trend of agriculture’s participation is econometrically proved. Dataset organized in graphs show grain and meat production steadily enlarged from 1970 to 2001, what is closely related to the productivity increase and federal grants to agriculture, despite the ratio of received/paid prices decreased during this 31 years. An accounting model is presented to show the main variables that determine agriculture’s participation in a country’s GDP and an econometric model is derived from this accounting model. Running this econometric model with 1973-2001´s US dataset, the following variables are the most important to determine the participation of agriculture in the US GDP: received/paid prices ratio, lagged value of agriculture’s participation in the GDP, and total factor productivity of the agriculture.