By the year 2050, there will be at least 9 billion people on Earth to feed using the same amount or less land and water than is available today. Currently, about one-third of all potential agricultural commodities grown worldwide are lost to diseases, weeds, insects and other pests. Farmers will be challenged to produce more, but to do so using sustainable cropping practices and less fertilizer and pesticides. Biological control is an integral part of sustainable agriculture. This chapter provides an overview of the topics of the construction, activity and use of transgenic biocontrol agents (BCAs) and their future potential in 21st century agriculture.