THE DEVELOPMENT OF RECOMBINANT DNA TECHNOLOGIES in the 1980s enabled the rst rational approaches to manipulate the metabolic capabilities of microbial cells. Initial strat-egies were directed at the manipulation of native pathways in microbial production hosts by overexpression or deletion of individual enzymes. Further developments in the eld of genetic engineering combined with an increasing understanding of metabolic processes on the molecular level has enabled more sophisticated metabolic engineering strategies including, for example, the assembly of multienzyme pathways composed of genes selected from dierent organisms. e analysis of metabolic uxes and their control has provided means to direct rationally and optimize a desired metabolic output by an engineered cell. Presently, the increasing availability of genomic information provides a seemingly limitless resource for new metabolic functions to be explored and implemented into engineered metabolic pathways for increased production levels and/or synthesis of new compounds. Despite the tremendous advances made in metabolic engineering during the last two decades, rational design eorts are still challenged by the complexity and redundancy of the cellular metabolic network as well as the lack of structural information and biochemical understanding of the metabolic enzyme(s). Recognizing these challenges, engineers have turned to nature as a guide for the development of new design strategies that mimic evolutionary mechanisms. Section I will introduce strategies and applications of evolutionary engineering as they apply to engineering of metabolic enzymes and networks.