PERT is a probabilistic project management technique developed by the U.S. Navy in the 1950s for the Polaris missile program. Unlike CPM which uses deterministic durations, PERT accounts for uncertainty using three time estimates for each activity: optimistic time (a), most likely time (m), and pessimistic time (b). Expected duration is calculated as: tₑ = (a + 4m + b)/6, with variance σ² = [(b-a)/6]². PERT enables probability analysis of project completion times using the Central Limit Theorem, assuming activity durations follow beta distributions.