A red letter day is any day of special significance or opportunity. Common red letter days of the year are marked in red in a calendar.
Red letter day may also refer to:
Film and television Red Letter Day (film), 2019 satirical horror film Red Letter Day (TV series), British anthology of teleplays, many by Jack Rosenthal
Music Red Letter Day (band), English punk rock band Red Letter Days (album), 2002 rock album by The Wallflowers Red Letter Day (EP), 1999 emo/pop punk EP release by The Get Up Kids "A Red Letter Day", single from the Pet Shop Boys
Other "A Red Letter Day", a chapter in the video game Half-Life 2 Red Letter Days, experiential gifts company in the UK Red ink, in hand lettering