A study has been made of the process of solidification of the alloys of tin and lead the eutectic structure of which is typically lamellar. A technique was developed in which the rate and direction of solidification were controlled. It was demonstrated that freezing takes place by the simultaneous edgewise growth of the lamellae, the thickness of which depends on the rate of freezing. It was also shown that the interface between solid and liquid at any instant is corrugated, owing to the fact that one of the phases is in advance of the other. This is attributed to the difference in thermal conductivity of the two phases. A detailed description is given of the process of eutectic solidification