Screening is normally the first unit operation utilized at a wastewater treatment plant. The purpose of screens is to remove large objects that can damage equipment, block valves, nozzles, channels, pipelines, and appurtenances. This creates serious plant operation and maintenance problems. Fine screens are gaining popularity as a substitute for preliminary and primary treatment to remove suspended solids and BOD. Applications of microscreens have also been developed for polishing secondary effluent or tertiary treatment. This chapter covers types of screening devices and their applications, course screens, design criteria and design examples, and more. Screening devices are widely used for wastewater treatment. They are broadly classified as coarse screens, fine screens, and microscreens.