Psalm 134 is the 134th psalm from the Book of Psalms, a part of the Hebrew Bible and the Christian Old Testament, beginning in English in the King James Version: "Behold, bless ye the LORD, all ye servants of the LORD". Its Latin title is "Ecce nunc benedicite Dominum". It is the last of the fifteen Songs of Ascents (Shir Hama'alot), and one of the three Songs of Ascents consisting of only three verses. The New King James Version entitles this psalm "Praising the Lord in His House at Night".

This psalm is Psalm 133 in the slightly different numbering system of the Greek Septuagint and Latin Vulgate versions of the Bible.

The psalm forms a regular part of Jewish, Catholic, Lutheran, Anglican and other Protestant liturgies. It has been set to music often and paraphrased in hymns. The short psalm is part of the daily Catholic service Compline, for which settings in Latin were composed by composers such as Tomás Luis de Victoria and Orlando di Lasso. It is frequently used in Anglican Evening Prayer, with settings by John Dowland and Benjamin Rogers, among others.

Nonconformist minister Matthew Henry notes that, as the last of the Songs of Ascents, this psalm serves as a fitting conclusion to the singing of all the Songs of Ascents in the Temple in Jerusalem which took place by the day, as it exhorts "the ministers to go on with their work in the night when the solemnities of the day were over". The psalm could also be interpreted as a "dialogue", as the priests and Levites who served in the Temple are enjoined in verses 1 and 2 to spend their time during the night watch in acts of devotion rather than small talk; and in verse 3 these devotees are urged to pray for the one who enjoined them in verse 1 – either the high priest or a captain of the night guard. A note in the Jerusalem Bible suggests that the dialogue involves pilgrims and temple ministers. Similarly, Baptist preacher Charles Spurgeon posits that verse 1 was recited by the festival pilgrims leaving the temple in the predawn darkness; seeing the guards with their lamps on the temple wall, they bid farewell to these loyal caretakers of the sanctuary. In return, the priests call out their blessing for the departing pilgrims in verse 3. Spurgeon extrapolates from this the need for congregants to pray for those who minister to them, and for ministers to pronounce blessings on their congregations.

The Midrash Tehillim connects the contents of this psalm to several Jewish practices. Rabbi Yochanan says that "servants of the Lord who stand in the house of the Lord at night" mentioned in verse 1 refers to those who engage in nighttime Torah study, which God considers in the same light "as if they occupied themselves with the priest's service in the house of the Lord". The midrash connects the lifting of the hands in preparation for blessing the Lord in verse 2 with the practice of lifting the cup of wine with both hands for the recital of the Birkat Hamazon (Grace after Meals). The midrash further connects this verse to the Priestly Blessing, as Rabbi Simeon ben Pazzi says that a Kohen who has not ritually washed his hands may not lift them to invoke the Priestly Blessing.

The Zohar also explains verse 2 as referring to the kohanim (members of the Jewish priestly class) who bestow the priestly blessing upon the congregation in the synagogue with raised hands. Before pronouncing the blessing, the kohanim must ritually wash their hands. They do not do so themselves; rather, the handwashing is performed by members of the levitical class, "who themselves are holy". If a Levite is not present in the synagogue, a firstborn son pours the water, since he too is called "holy".

Psalm 134 is recited in some communities following the Shabbat afternoon prayer between Sukkot and Shabbat Hagadol (the Shabbat before Passover). In the Siddur Avodas Yisrael, the entire psalm is recited before the evening prayer on weekdays. The psalm is also recited in full before engaging in Torah study.

Verses 1 and 2 are part of the penitential poetry of Selichot.