Time-dependent static light scattering (TDSLS) signatures were used to characterize polymerization reactions in situ. The relationship between these signatures and intra- and interparticle characteristics of the growing polymer population, as the solution passes from the dilute to semidilute regime, is sought theoretically, and measured experimentally. As much information as possible is determined concerning polymer mass and polymerization kinetics. At the outset of the reactions the weight-average molecular mass M-w dominates the scattered intensity, but gives way to second and third virial coefficient (A(2), A(3)) effects as polymer concentration increases. Since polymer mass, A(2) and A(3) are interrelated, it is possible to introduce plausible conversion kinetics to predict a variety of TDSLS signatures. These are calculated for free radical and controlled radical polymerization and compared to experimental TDSLS signatures for acrylamide free radical polymerization. These signatures are fit with only two eligible parameters; M, and the reaction rate constant a. Predictions concerning the evolution of Mw in a "dead-end" polymerization are also made and measured experimentally using an online monitoring method.