The United States Holocaust Memorial Museum describes Holocaust Remembrance Day this way:
The United States Congress established the Days of Remembrance as our nation’s annual commemoration of the Holocaust and created the United States Holocaust Memorial Museum as a permanent living memorial to the victims. This year Holocaust Remembrance Day is Sunday, May 1. The Museum designated Justice and Accountability in the Face of Genocide: What Have We Learned? as the theme for the 2011 observance.
I’ve just updated The Best Sites For Learning About The Holocaust.