Bacteria, fungi, algae, and protozoa are the microorganism classes of concern in cooling water systems. To control the growth of these organisms, programs employing oxidizing microbicides, nonoxidizing microbicides, and biodispersants are often used. This technical committee report discusses specific technologies used to control these classes of microorganisms. This report provides owners, engineers, contractors, and operators with specific information on the types of organisms found in cooling systems, a list of common chemistries used for their control, and methods that are typically employed to monitor systems. Its intent is not to serve as a guide to set up a microbiological control program, but to assist users in understanding the components of in-place programs and discuss the treatment program typically used to avoid misapplication. While this report includes a list of common technologies used to treat biofouling, it is not meant to be exhaustive.