Because of their graphics capabilities, it is possible to use personal computers to analyse the behaviour of dynamical systems. We therefore require a way to introduce pedagogically both this technique and the important aspects of the study of non‐linear systems. This paper considers first the formal points of the phase plane method, and then presents three relevant examples: (a) second order linear systems; (b) the Van der Pol oscillator; and (c) the forced pendulum. In each case programs in Turbo‐Pascal are given for plotting the trajectories.