This paper deals with a new appraisal of free radical polymerization modeling. Classical properties of the distribution of polymerization degrees and methods for studying them thanks to the z-transform are recalled. When simple mechanisms are involved, the kinetics may he represented by a "detailed analytic" model relying on macromolecule balances. This is no longer possible when complex processes are occurring, e.g. transfer to polymer, @-scission, terminal double bond propagation.. In order to deal with these more complex cases, a "tendency model" is proposed, relying on balances of quantities such as free radicals, macromolecules and the moments of the distribution of polymerization degrees. The quality of the polymer is described by chemical characters such as double bonds, long and short branching points, terminal double bonds., for which kinetic equations are estabtished. Equations are given for calculating the moments of free radicals and those of instantaneously produced macromolecules via various processes. The simplicity and the usefulness of the method are illustrated by several examples and a comparison is made, when possible, with the detailed approach. Finally, eouations are eiven. makine it nossible to calculate the ouality of polymer produced in any kind of reactor and for dikerent state; of skgregat&n. '