Many attempts have been made in the past to bring order to the near-bewildering array of eutectic morphologies. These have met with limited success due mainly to the fact that the morphology of a particular eutectic may be highly dependent on both chemical composition and the rate of freezing. This paper shows for binary alloys, at least, that a more complete understanding of eutectic growth may be obtained by applying a few simple 'rules'. With these it is possible to so characterize eutectic growth that the unknown structure of a particular eutectic may be predicted at a given growth rate if the entropy of solution and relative volume of each phase are known. The characterization scheme embraces the growth behaviour of the thirty or so systems for which thermodynamic data are more readily available.