Metabolic engineering is not another form of classic manipulation of intermediary metabolism; rather, it is the purposeful design of metabolic networks. The metabolic engineering approach examines biochemical reactions in their entirety, rather than individually, and is concerned with the construction of novel pathways, the thermodynamic feasibility of pathways, and the location of limiting branch-point(s) and enzymatic reaction(s) in a reaction network. The ultimate goal is the construction of strains with superior yield and productivity obtained through a convergent evolutionary process. Progress has been made toward this objective within the framework of Metabolic Control Analysis through the development of methodologies for the experimental determination of elasticities and flux control coefficients.