According to J. P. Flory, Nobel Prize laureate in 1974, all kinds of polymerization may be subdivided into two categories: chain growth polymerizations (CGPs) and step growth polymerizations (SGPs). This subdivision is based on kinetic aspects of the polymerization processes and not on thermodynamic aspects. The SGPs may again be subdivided into two groups, namely polycondensation and polyaddition, which are quite different from the thermodynamic point of view. Most polycondensations are characterized by a reaction entropy around zero, so that even SGPs with a small negative reaction enthalpy allow for syntheses of high molar mass polycondensates. This feature of SGPs arises from the fact that each condensation step which connects two molecules involves liberation of a new molecule, so that the balance of translational motion is zero.