Psalm 31 is the 31st psalm of the Book of Psalms, beginning in English in the King James Version: "In thee, O LORD, do I put my trust". In Latin, it is known as "In te Domine speravi". The Book of Psalms is part of the third section of the Hebrew Bible, and a book of the Christian Old Testament. In the slightly different numbering system used in the Greek Septuagint version of the Bible, and in its Latin translation, the Vulgate, this psalm is Psalm 30. The first verse in the Hebrew text indicates that it was composed by David.

The psalm forms a regular part of Jewish, Catholic, Lutheran, Anglican and other Protestant liturgies. Metrical hymns in English and German were derived from the psalm, such as "In dich hab ich gehoffet, Herr" and "Blest be the name of Jacob's God". The psalm has often been set to music, both completely and using specific sections such as "Illumina faciem tuam" (Make thy face to shine). Vocal settings were written by Johann Crüger, Heinrich Schütz, Joseph Haydn, and Felix Mendelssohn, among others.

"Into thine hand I commit my spirit" were the last words of many Christian figures, including Jesus, Saint Bernard, Jerome of Prague, and Martin Luther. "My times are in Thy hand" also became a frequently quoted phrase. Psalm 31:24 be strong and take heart all you who hope in the Lord.

"In te Domine speravi", the Psalm's first line in Latin, is also the final line of the ancient Te Deum hymn. Rendered in English frequently as, "O Lord, in thee have I trusted: let me never be confounded," the Te Deum in both the Latin and English texts have been set numerous times to music, notably by Hector Berlioz in Latin and John Rutter in English.

The author of the psalm is identified by the first verse in the Hebrew, "To the chief musician, a song of David". It was likely written while David was fleeing from Saul. On the basis of the wording of the Psalm, Charles and Emilie Briggs claim that "The author certainly knew Jeremiah, Isaiah, Ezekiel, and many Psalms of the Persian period. We cannot put the composition earlier than the troubles of Israel preceding the reforms of Nehemiah". The Persian period began in 539 BC, and Nehemiah's reforms are dated to about 445 BC.

In the psalm, David calls God his "rock" (which shields him from attack) and his "fortress" (which protects him on all sides). David also cites his physical ailments—"[h]is eyesight has dimmed from his troubles, and he has endured physical as well as spiritual deprivation. His life has been a continuous flow of trouble, causing him to age prematurely"—and acknowledges that these afflictions were sent by Heaven to encourage him to atone for his sins. The psalm ends on a note of hope: "The faithful should love G-d because He protects them, but He carefully repays the arrogant what they deserve".

In the New Testament, the four evangelists each cite the last words of Jesus; according to Luke the Evangelist, these last words came from verse 5 (KJV) of Psalm 31, "Into thine hand I commit my spirit". Similarly, according to nineteenth-century English Anglican bishop John James Stewart Perowne, this verse constituted the last words of many Christian figures, including Polycarp, Saint Bernard, Jerome of Prague, Martin Luther, and Philip Melanchthon. James Limburg notes that this makes the psalm suitable for preaching, and that it is often intoned at the time of death.

Verses 2–4 (in the Hebrew) are also the first 3 verses of Psalm 71. Jeremiah repeats the words magor mesaviv (Hebrew: מגור מסביב, "terror on all sides") from verse 14 (in the Hebrew; verse 13 in English Bibles) in Jeremiah and Lamentations.