. One of the strengths of Partial-Order Causal Link (POCL) planning is the ability to postpone decisions. But because postponed decisions play no role in reasoning about the plan until they are eventually acted upon, the penalty for postponing some decisions can be quite high. We call this style of decision postponement passive postponement, and present experimental results that quantify the efficiency penalty it incurs. We also suggest an alternate approach, active postponement, that allows postponed decisions to impose constraints on the generation of a plan. This constraint-based approach to decision postponement has been implemented in the Descartes planning system. In Descartes, every planning decision is represented by a variable, with constraints on each variable representing criteria that must be satisfied by the corresponding decision. These constraints are managed by a general-purpose constraint engine, so that even postponed decisions play a role in reasoning about the plan....