The real-time computer graphics rendering process embodies complex state transitions and fast dynamics amidst observable steady-state behaviour. This chapter describes the application of system identification methodology to real-time rendering. The basis for such an approach is that the rendering process may be treated from a system perspective as a data processing function. Current research in rendering workload characterisation and rendering time estimation strives to profile the attributes of rendering without providing a systematic way to control the process. Often, the user is expected to arrive at some form of a primitive control strategy based on profile information. The chapter discusses that linear time-invariant models can be obtained from the input and output data collected from experiments conducted using sample rendering applications. It reviews two experiments conducted to derive the system model of rendering processes and one experiment illustrating the use of a derived model in a control system.