This document presents the use of particle swarm optimization (PSO) technique to solve the economic load dispatch (ELD) problem in power systems. The ELD problem aims to schedule power plant generation outputs to meet load demand at minimum operating cost while satisfying constraints. PSO is applied by initializing generator outputs as "particles" that fly through search space to find minimum cost. Results on 5-unit and 6-unit test systems show PSO able to determine optimal outputs to meet time-varying loads at lowest cost within constraints.