Agrobacterium has been widely used as a vector to create transgenic plants. Agrobacterium-mediated gene transfer is governed by various factors of bacterial, host and environmental origin. Applications of this technology include enhancement of plant tolerance to biotic/abiotic stresses, increased crop productivity, pest resistance, phytoremediation, production of biopharmaceuticals, and enhanced nutritional content of crop plants. Agrobacterium has been successfully used to transform various economically and horticulturally important monocot and dicot species by standard tissue culture and in planta transformation techniques. Moreover, a novel Agrobacterium T-DNA-derived nano-complex method has been developed which will be highly valuable for plant biology and biotechnology.