The Federal Communications Commission has adopted a Notice of Inquiry (NOI) seeking comment on standards to distinguish between legitimate phone calls and those that engage in Caller ID spoofing. Although some carriers and third parties currently offer consumers various services to block or filter unwanted calls, the Commission continues to receive many consumer complaints about Caller ID spoofing and robocalls, and therefore wants to provide an additional tool for authenticating calls. A number of stakeholders, including members of the Internet Engineering Task Force (IETF), Alliance for Telecommunications Industry Solutions (ATIS), and SIP Forum, have developed protocols for validating calls to mitigate spoofing and fraudulent robocalling. In the NOI, the Commission requests feedback on implementing these standards, particularly the ATIS/SIP Forum proposals. The FCC also seeks comment on its governance role with respect to caller authentication, as well as related public policy considerations. Comments on the NOI are due by August 14, 2017, and reply comments are due by September 13, 2017.