This is a review paper on the effects of aluminum sulfate (alum) on ammonia volatilization and P runoff from poultry litter. Initially, laboratory studies were conducted that showed P solubility could be reduced in poultry litter with Al, Ca, and Fe amendments, indicating that these amendments may reduce P runoff. These results were confirmed in small plot studies in which alum applications to litter were shown to decrease P concentrations in runoff by as much as 87%, while improving tall fescue yields. Leaf tissue analyses indicated that the yield improvements were due to increased N availability, which we hypothesized was due to reduced NH3 volatilization. This result was confirmed in laboratory studies that showed that alum was one of the most effective (and cost-effective) compounds for reducing NH3 volatilization. Field trials conducted at commercial broiler farms in conjunction with the Environmental Protection Agency showed that alum additions to poultry litter lowered litter pH, particularly during the first 3 to 4 wk of each growout, which resulted in less NH3 volatilization and lower atmospheric NH3. Ammonia volatilization rates were reduced by 97% for the first 4 wk of the growout. Broilers grown on alum-treated litter were heavier than the controls (1.73 vs 1.66 kg) and had lower mortality (3.9 vs 4.2%) and better feed efficiency (1.98 vs 2.04). Electricity and propane use were lower for alum-treated houses. As a result of these economic benefits to the integrator and grower, the benefit:cost ratio of alum addition was 1.96. Phosphorus concentrations in runoff from small watersheds were 75% lower from alum-treated litter than normal litter over a 3-yr period. Long-term small plot studies on alum use have shown that alum-treated litter results in lower soil test P levels than normal litter and does not increase Al availability in soils or uptake by plants.