The LIBOR is the most widely used index for adjustable rate mortgages (ARMs). At the end of 2021 it will cease to exist or become unreliable. While mortgage contracts give noteholders the authority to replace the index, it has not been done on such a scale, and the standard contract language is problematic. The Alternative Reference Rate Committee (ARRC) has made recommendations for a new index and for the transition, but the ARRC’s recommendations are only voluntary.