A farm survey was conducted in southern India, the central Tarai of Nepal, and the northern Philippines to determine the economics of, and farm-level constraints in, the adoption of green manure (GM). Negative short-term benefits from GM were obtained in India and Nepal, but these were positive in the Philippines. Green manure may be economical in the long run if evaluated in absolute terms. However, when it was compared with other options available to farmers, for example, legume production in India and Nepal, the legumes gave higher income and were equally beneficial in sustaining resource productivity over time. Availability of seed, lack of irrigation water, and high incorporation costs were identified as the constraints to the adoption of GM. It was observed that, even when these constraints were relaxed, farmers did not adopt GM cultivation as other options were economically more attractive. Therefore, economic non-viability of GM, under the existing fertilizer, labour, and land prices, is the major constraint. Further research on GM should examine the economic and nutritional use of GM species as food and fodder, and aim at increasing the yield potential of existing grain legume species to enhance their short-term benefits and allow the long-term benefits to follow.