This chapter gives a brief introduction to the biotechnological techniques which have been used for transforming genomes of plants and plastids. The aim of the engineering methods is to transfer a piece of a species-alien DNA molecule into the genome of a selected species providing the species with a new function or an altered function. The transfer methods all depend on the successful incorporation of the alien DNA into the genome of the species, on the expression of the gene and on the transfer of the gene to the next generation.