The rice-wheat cropping system was rapidly adopted in South Asia after the development of input-responsive, high-yielding varieties of both crops in the 1960s and 1970s. This became one of the world's major food production systems, occupying about 20 million ha and providing staple grains to more than 1 billion people. However, the rice-wheat system is under stress today. Diminishing yields in long-term experiments (Duxbury et al 2000), stagnating farmer yields, and declining factor productivity (Hobbs and Morris 1996) indicate that the sustainability of the rice-wheat system is questionable. Neither farmers nor researchers are sure of the reasons for the alarming trend. Since 1994, the Rice-Wheat Consortium for the Indo-Gangetic Plains-composed of national agricultural scientists from Bangladesh, India, Nepal, and Pakistan, advanced research institutions, and international agricultural research centers-has been working to address sustainability concerns about the rice-wheat cropping system (Gupta et al 2003).