Plant genetic engineering will probably contribute to the required continued increase in agricultural productivity during the coming decades, and moreover, plants can potentially provide inexpensive production platforms for pharmaceuticals and nutraceuticals. With the advent of technologies for altering the genetic information inside chloroplasts, a new attractive target for genetic engineering has become available to biotechnologists. Potential advantages over conventional nuclear transformation include high transgene expression levels and increased biosafety because of maternal organelle inheritance in most crops. This review summarizes the state of the art in chloroplast genetic engineering and describes how reverse genetics approaches enhance our understanding of photosynthesis and other important chloroplast functions. Furthermore, promising strategies by which chloroplast genetic engineering might contribute to the successful modification of plant metabolism are discussed.