This Topic introduces the concept of calculating the stochastic process at the output of a known deterministic system, given a stochastic process at the input of the system. This concept is approached by considering the operation of the system on each realisation of the input stochastic process, and calculating the statistics over the resulting ensemble at the output. The video discusses why it is necessary, in this course, to restrict the analysis to known linear time-invariant (LTI) systems with wide-sense stationary (WSS) inputs. An overview is provided for the four different methods for calculating the input-output statistics, namely in the time-domain or frequency-domain, and either using the system impulse-response or the system-difference equation. Finally, an example of simulating the ensemble statistics through a Monte Carlo experiment is shown.