Evolutionary biologists hypothesize that ancestral enzymes were generalists, that is, that they catalyzed several related reactions. Starting from these stem cell–like enzymes, evolution created today’s specialist enzymes that efficiently catalyze mainly one reaction. Using the current understanding of evolution, evolutionary biologists can reconstruct likely ancestors of current enzymes and, using gene synthesis, resurrect these enzymes in the laboratory. Current studies of resurrected ancestral enzymes seek to answer basic questions of how new enzymes and metabolic pathways evolve. In addition, resurrected ancestral enzymes may be starting points for protein engineering because ancestral enzymes can catalyze additional chemical reactions, including potentially useful unnatural reactions. This symposium brings together evolutionary biologist and protein engineers.