Peasant agriculture in the tropics assumes ever greater importance, but relevant experiments are difficult to conduct, partly because existing techniques were evolved for single crops, whereas smallholders may use several crops together. Also, the concern of smallholders is to minimize the risk of crop failure rather than to maximize average yields. Methods are suggested for evolving and assessing new intercropping systems and for predicting how far they will succeed under different conditions. How an intercrop works, and selection of crop varieties to be used, are also discussed.