The post-genomic era of medicine will be defined by our ability to achieve biological control through genetic reprogramming. New tools are needed to accurately rewrite the three billion base pair human genomic script and specifically alter genes, gene expression, and epigenetic state at any desired loci. To date, no enzyme - natural or synthetic - has been able to accurately modify only a single targeted site within the human genome. Recently, our studies have focuses on the development of a general strategy for the design of enzymes that target a single site within the genome. We generated chimeric zinc finger recombinases with cooperative DNA-binding and catalytic specificities that integrate transgenes with >98% accuracy into the human genome. These modular recombinases can be reprogrammed: New combinations of zinc finger domains and serine recombinase catalytic domains generate novel enzymes with distinct substrate sequence specificities. Because of their accuracy and versatility, the recombinases/integrases we are developing should be suitable for a wide variety of applications in biological research, medicine, and biotechnology where accurate delivery of DNA is desired.