The occurrence of the ubiquitous and intriguing "ordinary-extraordinary" behavior of dynamics in solutions of charged macromolecules is addressed theoretically by explicitly considering counterions around the macromolecules. The collective and coupled dynamics of macromolecules and their counterion clouds in salt-free conditions are shown to lead to the "ordinary" behavior (also called the "fast" mode) where diffusion coefficients are independent of molar mass and polymer concentration and are comparable to those of isolated metallic ions in aqueous media, in agreement with experimental facts observed repeatedly over the past four decades. The dipoles arising from adsorbed counterions on polymer backbones can form many pairwise physical cross-links, leading to microgel-like aggregates. Balancing the swelling from excluded volume effects and counterion pressure with elasticity of the microgel, we show that there is a threshold value of a combination of polymer concentration and electrolyte concentration for the occurrence of the "extraordinary" phase (also called the "slow" mode) and the predicted properties of diffusion coefficient for this phase are in qualitative agreement with well-known experimental data.ordinary-extraordinary transition | slow mode | fast mode | polyelectrolyte dynamics | polyelectrolyte aggregation T he "ordinary-extraordinary" transition has been known over the past four decades from dynamic light-scattering (DLS) experiments on aqueous solutions of charged macromolecules such as DNA, polylysine, polystyrene sulfonate, polyvinyl pyridine, etc. (1-22). In the so-called "ordinary" behavior, the diffusion coefficient D determined from DLS increases, from the value D SE expected from the Stokes-Einstein law for dilute polyelectrolyte solutions at high enough monovalent salt concentrations c s sufficient to screen electrostatic interactions, to even higher values upon a decrease in c s . This observation is already intriguing, because the chain swells due to stronger intrachain electrostatic repulsion at lower values of c s and hence D is expected to decrease according to the Stoke-Einstein law. However, D actually increases! Even more strangely, upon further decrease in c s , an additional diffusion coefficient with very small values emerges, suggesting the presence of large aggregates. It is surprising that similarly charged, and hence electrostatically repulsive, polymers would aggregate at all and that they would break apart when electrostatic repulsion is screened by added electrolyte. In view of this mysterious nature, this behavior is called "extraordinary." In addition to these tantalizing facts, the occurrence of the ordinaryextraordinary behavior for solutions of charged macromolecules completely undermines the utility of the Stokes-Einstein law, which is the routine methodology for characterizing uncharged macromolecules in solutions.The diffusional modes corresponding to the ordinary and extraordinary behaviors are also called "fast" and "slow" modes, with their respective diffusio...