A wide variety of active fire protection systems are available to fire safety practitioners. In addition to passive fire protection measures, some level of active fire protection is normally required to meet the expected minimum level of fire safety in modern buildings. Active fire protection can also be used to increase the fire safety in order to achieve a more flexible fire safety design and an acceptable level of fire safety in buildings. There are many types of active fire protection systems, but this chapter deals mainly with automatic fire sprinkler systems, since they are often used to facilitate the use of timber as structure, internal linings and external facades in large or complex buildings. Sprinklers are required in some countries for taller timber buildings, as described in Chapter 4.