The semi-arid tropics are characterized by unpredictable weather, limited and erratic rainfall and nutrient-poor soils and suffer from a host of agricultural constraints. Several diseases, insect pests and drought affect crop productivity. Developing stress-resistant crops has been a worthwhile activity of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). Mandated crops of ICRISAT, including groundnut, pigeonpea, chickpea, sorghum and pearl millet, are the main staple foods for nearly one billion people in the semi-arid tropics. Genetic transformation provides a complementary means for the genetic betterment of the genome of these crops. Judicious application of biotechnological tools holds great potential for alleviating some of the major constraints to productivity of these crops in the agricultural systems of the semi-arid tropics. This article reviews plant genetic engineering in relation to its applications in genetic enhancement and the improvement of important crops of the semi-arid tropics. For the benefit of nonbiotechnologists, a brief review of technical aspects of plant genetic engineering is also included.