Many real‐life treatments are of limited supply and cannot be provided to all individuals in the population. For example, patients on the liver transplant waiting list usually cannot be assigned a liver transplant immediately at the time they reach highest priority because a suitable organ is not immediately available. In settings with limited supply, investigators are often interested in the effects of treatment strategies in which a limited proportion of patients receive an organ at a given time, that is, treatment regimes satisfying resource constraints. Here, we describe an estimand that allows us to define causal effects of treatment strategies that satisfy resource constraints: Incremental Propensity Score Interventions for limited resources (IPSIs). IPSIs flexibly constrain time‐varying resource utilization through proportional scaling of patients' natural propensities for treatment, thereby preserving existing propensity rank ordering …