While enzymes can be studied from the viewpoint of (a) the active site environment, (b) the kinetic mechanism, and (c) the chemical mechanism, an enzyme is a unit and all these approaches tell valid but partial tales. A complete understanding of enzyme mechanisms requires a correlation of these and other information, like enzyme structure and its dynamics. Although chemical mechanisms have been elucidated for many enzymes, how they achieve a catalytically competent state has become approachable only recently through experiments and computation. The synergy between structure and plasticity results in the unique power of enzymes. Structural enzymology aims to address these catalytic motions in detail.