The effect of heat input from laser beam welding (LBW) on the microstructural evolution of superalloy Inconel 718 was investigated. LBW was carried out on 1.6-mm-thick sheets with an average grain size of 13 mu m (ASTM # 9.5), and four different heat inputs in the range of 74.5 mm(-1) to 126.6 J mm(-1) were used. Full penetration was achieved in all weld experiments. Microstructures of the welds were evaluated using an optical microscope and a field emission scanning electron microscope. Increasing the heat input changed the resulting weld shape from a wine glass shape to a stemless glass shape with wider surface bead widths, and the measured average dendrite arm spacing was increased from 1.06 mu m to 2.30 mu m, indicating the corresponding solidification rate in the range of 1.75 x 10(5) K s(-1) (degrees C s(-1)) to 3.5 x 10(6) K s(-1) (degrees C s(-1)). The welds also were free from microfissuring even at the lowest heat input trials. The Nb concentration of Laves phase for the current LBW samples was approximate to 20.0 wt pct. The coefficients of partition and distribution for Nb were determined to be approximately 3.40 and 0.50, respectively.