The authors would like to acknowledge William Parker, MD, PhD, Assistant Professor of Pulmonary and Critical Care Medicine and the Assistant Director of the MacLean Center for Clinical Medical Ethics at the University of Chicago, for contributing new Covid-19 specific content to this edition of Clinical Ethics. Dr. Parker is a medical ethicist, pulmonary intensivist, and health services researcher who studies the allocation of scarce medical resources where demand greatly exceeds supply and healthcare systems cannot avoid overt rationing.