This chapter focuses on practical applications of the microbial genetic principles discussed in previous chapters. Although we have been altering the genetic makeup of organisms for centuries and nature has been doing it even longer, only recently have we been able to manipulate DNA directly using genetic engineering or recombinant DNA technology. The potential benefits of these techniques are great and affect such diverse areas as medicine, agriculture, and industry. However, the use of these techniques is not without risks, and these risks must be considered in any discussion of this technology.