It is well recognized within the telecommunications industry that illicit and nuisance calling, specifically illegal scam robocalls, has led to a significant loss of customer trust in the global telephone network. To restore this trust, carriers and service providers (SPs) have gone to considerable lengths to design and deploy services that will mitigate the impacts of these illicit calling campaigns. This report aims to provide a detailed summary of both the many types of illicit calling and the measures being deployed to counter them. It explains why there is no "silver bullet" that will instantly and forever eliminate all illicit robocalling and why, instead, the industry must deploy many separate components in combination to maximize mitigation with minimal blocking of wanted calls. A summary is included of the various U.S. actions and some international regulators to assist carriers and SPs in this effort. As these bad actors continue to evolve their techniques, further countermeasures will need to be developed to cope with these new threats. Accordingly, this report concludes with recommendations for future action by the Alliance for Telecommunications Industry Solutions (ATIS) and other organizations.