This paper provides an assessment of the agricultural diversification trends in South Asia. In the first part food consumption and crop production patterns in the region during the last twenty years are reviewed. Next, the agronomic and economic options for and constraints to diversification in the main agricultural systems are discussed based on a framework for assessing the flexibility of ricelands and rice farmers to respond to the commercialisation trends through seasonal or permanent diversification out of various farming systems. The principal contribution of this paper is to draw attention to some neglected aspects of diversification, especially the biophysical and economic constraints to the process in different farming systems. The flexibility of farmers in responding to diversification opportunities is constrained by the size of markets and price risks, soil suitability and land rights, the availability and quality of irrigation infrastructure, and the availability and cost of labour. Long term strategies to facilitate a smooth transition to commercialisation are recommended.