Fault-free lamellar structures were grown in eutectic thin films of Pb-Sn, Cd-Pb, and Al-Al2Cu. The 2 μ thick films were directionally solidified by either a scanning laser or a quartz iodine lamp. A thermal gradient at the solid-liquid interface was estimated to be 8000°C/cm for the laser heat source compared to 200°C/cm for the lamp. In each alloy the lamellar spacing was larger than values estimated from previous experiments with bulk material. Defects in the films were observed to generate V-shaped waves of bent plates that provide a mechanism for increasing the lamellar spacing. Computer-simulated microstructures for two dimensional lamellar growth were made by calculating the diffusion in the liquid ahead of an irregular lamellar structure assuming a planar interface, finding the shape of the solid-liquid interface, and finding the trajectories of the three phase junctions. The mechanism of two-dimensional eutectic growth was discussed.