In biochemistry, Michaelis–Menten kinetics, named after Leonor Michaelis and Maud Menten, is the simplest case of enzyme kinetics, applied to enzyme-catalysed reactions of one substrate and one product. It takes the form of a differential equation describing the reaction rate  (rate of formation of product P, with concentration ) to , the concentration of the substrate  A (using the symbols recommended by the IUBMB). Its formula is given by the Michaelis–Menten equation:
, which is often written as , represents the limiting rate approached by the system at saturating substrate concentration for a given enzyme concentration. The Michaelis constant  is defined as the concentration of substrate at which the reaction rate is half of . Biochemical reactions involving a single substrate are often assumed to follow Michaelis–Menten kinetics, without regard to the model's underlying assumptions. Only a small proportion of enzyme-catalysed reactions have just one substrate, but the equation still often applies if only one substrate concentration is varied.