During the past 30 years, automatic sprinkler systems have come a long way. With better testing and research and new and improved technologies, protection designs have emerged that can control fire in almost any situation. Unfortunately, many sprinklered buildings have still burned, causing millions in unnecessary property damage and business interruption. Understanding the basic concepts of fighting fires in sprinklered buildings can be challenging. Firefighters need to understand the building and occupancy, along with its fire protection systems, as part of preincident planning, not during size-up activities. A properly designed and installed fire protection system can protect the building, its contents, and its employees. The fire service should be involved during the sprinkler system design stage and throughout the life of the building to best understand how to interact with the system if and when a fire occurs. In the best-case scenario, firefighting operations in a sprinklered building only need to consist of completing final extinguishment of the fire, managing the sprinkler system, and performing salvage and overhaul operations. Letting the system work as designed can greatly reduce property damage.