In this chapter a new method of identifying the parameters of nonlinear circuits has been presented, based on the concepts of synchronisation of nonlinear circuits. The new procedure has been formulated as a global optimisation problem and it has been solved by using a genetic algorithm. The method has been applied to the estimation of the five dimensionless parameters of the chaotic Chua's oscillator and three experimental examples have been reported. The accuracy of the method has also been discussed. The advantages of the introduced algorithm are numerous; among these is its intrinsic low sensitivity to noise due to the robustness of the synchronisation framework. With the proposed approach a circuit model for chaotic behaviour could be obtained. In fact, many different attractors have been observed in nonlinear circuits and the introduced strategy represents a useful tool for determining the parameters of a circuit model which best fit a chaotic time series. Moreover, it could be used to estimate the parameters of the nonlinear circuit used as a modulator in a chaotic carrier cryptography system.