Plant transformation is the process by which DNA is introduced into plant cells or tissues. The DNA can come from virtually any source. Gene transfer methodology has become part of an essential technology to manipulate plants for both scientific and commercial purposes. Transgenic plants, the products of this methodology, are useful for dissecting the mechanism(s) of plant gene regulation. This technology is also useful for identifying and evaluating agriculturally useful traits (genes) as well as for their introduction into commercially valuable crops. One of the most efficient methods for gene transfer employs Agrobacterium tumefaciens and takes advantage of the naturally evolved crown gall-inducing mechanisms of DNA transfer present in this common soil pathogen. Much has been learned about the mechanisms of this form of DNA movement and subsequent crown gall induction. This information has been applied to develop methods that result in the formation of gall-free, genetically transformed plants. This chapter describes a detailed protocol for Agrobacterium-mediated transformation of tobacco cells and their subsequent selection and regeneration into transgenic plants.