This report analyzes and summarizes available data from 2015 to 2020 for accountable care organizations (ACOs) under the Medicare Shared Savings Program (MSSP). The aim is to provide relevant, timely, and useful information about the state of the MSSP ACO market. Results are summarized on a composite basis for all ACOs except where otherwise noted. We also highlight differences between various types of ACOs where relevant. Detailed data on the ACOs are included in two appendices.