Comprehensive counterion activity studies have revealed clear influence of the polyelectrolyte concentration and chain length on the polyion-counterion interaction, neither of which is evident from the existing theoretical models. The counter-ion activity coefficient (f(a)) increases below the overlap concentration c* as calculated from Odijk's scaling approach. At dilutions where the Debye length (l(D)) exceeds the contour length (L), this increase is more pronounced. It is concluded that these changes in the ionic interactions are primarily responsible for the strong increase of the equivalent conductivity (Lambda) below c*. The findings are not restricted to oligomers but apply to all chain lengths of polyelectrolytes at concentrations less than c*. The correlation of f(a) and Lambda with both c* and the ratio l(D)/L leads to a general description of polyelectrolyte behavior. Experiments were performed above and below c* and over the range 0.1 less than or equal to l(D)/L less than or equal to 10 using a series of poly(vinylbenzyltrialkylammonium) model polyelectrolytes with contour lengths over a range 7 nm less than or equal to L less than or equal to 102 nm and characterized by a charge density parameter xi = 2.85.