Increases in agricultural productivity contribute to national economic development and income growth in two major ways: they release labor resources for nonagricultural sectors and they supply an economic output above that consumed or used for further production in the agricultural sector-an "economic surplus" that can be transferred out of agriculture to provide capital for economic growth in the nonagricultural sectors. This paper suggests ways of measuring changes in agricultural output, input, and productivity and the contribution that increases in agricultural productivity can make to national income growth. Like Singer's article, it deals with mechanical aspects of economic growth? It suggests an analytical framework for research on conditions influencing improvement in agricultural productivity.