Many industrial processes, like kilns and boilers, discharge spent gases to the atmosphere. These gases, called "flue gases," are often treated to remove pollutants in order to meet environmental regulations. Sometimes, enough particulate is recovered that it is worth returning to the process. An electrostatic precipitator, or ESP, is one method for removing particulate matter from flue gas. This module will describe the major components as well as the purpose and operating principles of an electrostatic precipitator.