The objective of this paper is to identify the molecular parameters that govern ordering kinetics in a diblock copolymer melt. Experimental data on the ordering kinetics were obtained by time-resolved depolarized light scattering after the sample was quenched from the disordered to the ordered state. The ordered state consisted of cylinders arranged on a hexagonal lattice. During the early stages of the disorder-to-order transition, a dilute suspension of ordered grains grow by invading the surrounding, disordered phase. A time-dependent Ginzburg-Landau model was used to relate the growth rate of these grains to molecular parameters. The growth rate is predicted to be proportional to the quench depth and chain radius of gyration and inversely proportional to the molecular relaxation time. Independent estimates of these parameters were obtained from small angle neutron scattering and rheological measurements. The experimentally determined grain growth rates are in good agreement with theoretical predictions, with no adjustable parameters.