The approach yields the following relation. for the relative viscosity eta(rel) as a function of polymer concentration c (mass/volume): In eta(rel) = (c) over tilde/(1 + p (c) over tilde + q (c) over tilde (2)). Reduced concentrations (c) over tilde (defined as (c) over tilde = c[eta], where [eta] is the intrinsic viscosity) are used instead of c to incorporate thermodynamic information. The parameters p and q account for changes in the free volume of the solvent caused by the polymer. The analysis of literature data for seven very dissimilar systems discloses the following common feature: p > 0 and q < 0. This means that the curves in the plots of In eta(rel) as a function of <(c)over tilde> are normally located below the tangent at low (c) over tilde and above it at high (c) over tilde. The Amines of p and q correlate strongly with the temperature distance to the glass-transition temperature of the polymer (T-g). Beyond the Mere modeling of viscosity data, the approach allows the determination of [eta] from data at high polymer concentrations and provides information on the generalized intrinsic viscosity, {eta}. Measurements for T < T-g give access to glass curves, i.e to T-g(c). Moreover,, the modeling helps to recognize systems with special behavior,, such as solutions of poly(dimethyl siloxane) in its oligomers.