Sleepers Awake (also known as Wachet auf, ruft uns die Stimme, BWV 645) is a chorale cantata J.S. Bach composed in 1731 for the 27th Sunday after Trinity, which fell on the 25th of November that year. That was a year when Easter came unusually early, because it's not often the calendar has twenty-seven Sundays after Trinity, so thankfully this piece has become a popular part of Advent.
Many hymnals have a version of it. The the 1940 Episcopal hymnal, the OPC's Trinity Hymnal, the LCMS's Lutheran Worship, and the UMC's 1989 hymnal all share Catherine Winkworth's 1858 translation, called "Wake, Awake, for Night Is Flying."
The Cyber Hymnal provides an 1864 translation by Frances E. Cox called "'Sleepers, Wake!' The Watch Cry Pealeth," and in 1982 Carl P. Daw, Jr, translated it anew, calling it "'Sleepers, Wake!' A Voice Astounds Us," for the hymnal that was published that year.
I had always assumed that the cantata was written first and the hymn was taken from it, but it turns out that it's exactly the other way around!
Philipp Nicolai was a Lutheran minister and hymnwriter who lived through an outbreak of the plague in the late 1500s. He lost 170 of his parishioners in one week alone, and in 1598, to comfort those who remained, he wrote a series of meditations called The Mirror of Joy, which contained this hymn.
I believe this is the original version of it:
I've been all over YouTube the last couple of days listening to dozens of lovely renditions of this hymn and of the cantata -- far too many to put into one blog post -- so I will post a few more of my favorites as the week goes on. In the meantime I'll leave you with this, a congration singing it in Lituanian to the melody as originally composed by Philipp Nicolai.