To contain health care cost increases, Massachusetts enacted Chapter 224 in 2012, which established a first‐in‐the‐nation target, called a benchmark, for annual growth in total statewide health care spending. Among other things, the law created a Health Policy Commission and granted it authority to hold payers and providers accountable for keeping annual cost growth below the benchmark. This report shares findings from the study including lessons and considerations for state policymakers about the design and use of accountability mechanisms to meet a health care cost growth benchmark.