The report defines the relationship between scale formation and scrubber chemistry, based on thermodynamic analyses and bench-scale scrubber experiments, and includes a review of scaling problems in limestone wet scrubbing systems. It is assumed that mechanical scale deposition (due to wet/dry interfaces, stagnant areas, or poor gas/liquid distribution) can be controlled by good engineering design. Approaches to controlling chemical scale deposition are: pH control, highL/G, seeding, high residence time in a holding tank, temperature control, and oxidation control. It is shown that SO2 removal efficiency is a linear function of pH for 0.5% CaSO3 slurries, 0.5% CaCO3 and 0.6% limestone slurries, and 1% CaCO3 slurries. The CaCO3 scrubbing system is non-scaling, but removal efficiencies are limited by the SO3/HSO3 equilibrium to about 50%. In CaCO3 scrubbers, SO3 scaling can be minimized. A 100-125F temperature increase seems to increase the rate of scale deposition and, in the presence of O2, can lead to catastrophic scaling via a cementing reaction initiated by the precipitation of anhydrite. (Modified author abstract)