Cotton gins use air to move seed cotton, lint, cottonseed, and trash through conveying pipes. In gins, pneumatic conveying systems are the principal means of moving material from one processing stage to another throughout the entire ginning plant. Further, material drying or moisture restoration can be accomplished by heating or humidifying the conveying air. Pneumatic systems are a critical and fundamental component of cotton ginning. Cotton gins use large quantities of air for pneumatic conveying. It is common for a gin to use 4,248 m3 (150,000 ft3) or more of air per minute in its various material conveying systems. Because the density of dry standard air is approximately 1.2 kg/m3 (0.075 lb/ft3), a typical gin using 4,248 m3/min (150,000 ft3/min) of air moves 305,860 kg (675,000 lb) of air per hour. This mass of air per hour is approximately 1.5 times the total mass of material handled per hour. Typically, more than 60 to 65% of the total electrical power consumed by a cotton gin is attributed to moving material pneumatically. Properly taking air measurements, determining air flow requirements, sizing conveying pipes, sizing fans to generate required air flow rates, and accounting for specific machinery air requirements are essential to maximizing machine utilization, minimizing energy costs, and decreasing system downtime. This update of the Cotton Ginners Handbook provides current technical information on cotton gin pneumatic systems. It draws heavily on previous versions of the Cotton Ginners Handbook (Stedronsky 1964; McCaskill et al., 1977; Baker et al., 1994) and the knowledge and experience of current and past instructors of the Air Systems classes from the National Cotton Ginners’ Association Gin Schools.