When does the regulatory aftercare or post-closure care (PCC) period at a closed municipal solid waste (MSW) landfill end? There are few examples of existing regulations that provide clear guidance. However, this paper reports on an observed trend toward defining completion of PCC in terms of performance and functional stability (no unacceptable threat to human health or the environment in the absence of active care under regulatory oversight) rather than demonstrating organic stabilization of the waste mass (a largely theoretical state of degradation that is difficult to measure and monitor). Given growing acceptance of performance-based approaches on the part of some regulatory and regulated communities, this paper describes application of a performance-based methodology to evaluate progress toward functional stability at three case study landfills, two in USA and one in France. The evaluations provided reasonable outcomes for demonstrating functional stability across leachate and gas management systems in a period of time less than 30 years, and point to completion of settlement that could impact cap integrity in a significantly shorter period. Due to scope limitations, this paper does not consider the time required for monitoring to confirm no impact to groundwater or other potentially impacted media subsequent to transition to passive care; however, this monitoring should be recognized as critical to the process of completing a functional stability demonstration.