Concerns with chlorine disinfection have led to investigation of alternative disinfectants for use in the environmental arena. Are there environmentally safe alternatives to chlorine? Is peracetic acid one among these? Peracetic acid is one among several chemicals that have been touted as a replacement in recent years. Peracetic acid is very effective in killing bacteria, viruses, fungi, and spores over a wide pH and temperature range. Organic matter or storage time does not reduce the effectiveness of peracetic acid. The breakdown products of peracetic acid, hydrogen peroxide and acetic acid are reported to be environmentally friendly. This factor, along with recent improvements in stabilization techniques allowing longer storage periods and decreased costs have peaked the interest in peracetic acid as an alternative chemical for disinfection in the water and wastewater fields. Recent studies have discussed peracetic acid as an alternative chemical to chlorine for drinking water; wastewater treatment plant effluent and combined sewer overflow (CSO) disinfection. Advantages of peracetic acid over chlorine include lower chemical needs, shorter contact time, and its ability to be effective in the presence of organic matter. Another advantage is the absence of disinfection byproducts, which has led water and wastewater treatment professionals to believe that a quenching facility (i.e., similar to dechlorination) is not required. Our experience and research has shown that it is a very potent chemical that can have negative impacts. Due to its high potency, it is very important to use utmost caution when applying this in CSO or treatment plant effluent disinfection applications. One of the biggest advantages of peracetic acid, i.e., its stability, is its greatest disadvantage in such applications. The breakdown products may be environmentally friendly, but it takes a very long time for peracetic acid to decompose. Stabilizers used in the preparation of peracetic acid enable dilute solutions to maintain activity for a number of days. Consequently, excess chemical used in effluent and/or CSO disinfection remains active for a long time and can negatively affect receiving waters, continuing to kill microorganisms unless the excess chemical is quenched. Therefore, it is extremely important to determine the impacts of peracetic acid on microorganisms in the receiving water body and to evaluate the need for quenching. Dechlorination chemicals such as sodium bisulfite are effective in quenching peracetic acid also.This paper summarizes our experiences with peracetic acid. Based on experience and research over the years, pros and cons of using peracetic acid as an alternative disinfectant will be summarized.