"A Red Letter Day" is a single by British electronic music group Pet Shop Boys. It was released the fourth single from their 1996 album Bilingual on March 17, 1997. The single peaked at high #9 on the UK Singles Chart, making it another top 10 single for the group. However it then fell straight out the UK top 40 (to #42) the following week. At the time, this was a record as the biggest such fall to ever occur in UK chart history, but it was then beaten five months later by Embrace with their single "My Weakness is None of Your Business" (which fell from #9 to #44 the following week).

The duo were big admirers of the Motiv8 sound who had remixed various other artists at the time. Neil Tennant asked the man behind Motiv8 (Steve Rodway) to remix this single. He even went to visit Rodway at work in his studio during the remix. Ironically after it was finished and delivered, Tennant insisted a synth line which Rodway had come up with on the Motiv8 version, should be used on the Pet Shop Boys' own main mix. After trying unsuccessfully to recreate Rodway's riff it eventually had to be sampled from the Motiv8 mix, thus it appears on both the Pet Shop Boys' main version as well as the Motiv8 remix.

A red letter day (sometimes hyphenated as red-letter day or called scarlet day in academia) is any day of special significance.

The term originates from Medieval church calendars. Illuminated manuscripts often marked initial capitals and highlighted words in red ink, known as rubrics. The First Council of Nicaea in 325 decreed the saints' days, feasts and other holy days, which came to be printed on church calendars in red. The term came into wider usage with the appearance in 1549 of the first Book of Common Prayer in which the calendar showed special holy days in red ink.

Many current calendars have special dates and holidays such as Sundays, Christmas Day and Midsummer Day rendered in red colour instead of black.

On red letter days, judges of the English High Court (Queen's Bench Division) wear, at sittings of the Court of Law, their scarlet robes (See court dress). Also in the United Kingdom, other civil dates have been added to the original religious dates. These include anniversaries of the Monarch's birthday, official birthday, accession and coronation.