Tehillim · The book of Tehillim
What is the Psalm of the day (shir shel yom)?
The Psalm of the day is the psalm assigned to each day of the week — the very one the Levites sang in the Temple — recited after the morning service (Shacharit).
A different psalm for each day
Every day of the week carries its own psalm, the שיר של יום (shir shel yom), the song of the day. These are the very psalms the Levites sang upon their platform in the Temple, one appointed for each day. We say the day's psalm after the morning service (Shacharit), and in doing so we keep the Temple's music alive in ordinary time.
Where this comes from
The Mishnah records this in tractate Tamid 7:4, the chapter that describes the daily Temple service and names the song the Levites sang on each day of the week. What was once sung by them we now say in prayer, so that the week itself is counted in psalms.
What to do
After the morning service, say that day's psalm — each day from the first of the week through Shabbat has its own. A siddur (prayer book) will show you the psalm appointed for today.
Source: Mishnah, Tamid 7:4.
If you are not sure which psalm belongs to today, Kolí (the Tehillim for the moment you are living) knows the day and brings you its song.
Open Kolí