Notes (NET Translation)
The LXX, Vulgate, and Roman Catholic Church count Psalms 9 and 10 as one pslam, while the Protestant churches follow the Hebrew reckoning in considering Psalms 9 and 10 separate psalms. For this reason, the numbering of the psalms from this point to Psalm 148 may be off by one depending on what numbering your source is using.
The following points are used to treat the two psalms as one psalm:
- Psalm 10 lacks a title/superscription.
- The acrostic device begun in Psalm 9 continues in Psalm 10.
- Both psalms share similar vocabulary.
- The LXX and Vulgate (and some Hebrew manuscripts) treat them as one psalm.
The following points are used to treat the psalms as separate psalms:
- Both psalms seem complete in their own right.
- The acrostic device is incomplete in both psalms (letters are skipped).
- The mood seems to change in Psalm 10.
It is not clear that the two psalms were once one psalm. Regardless of how one views this matter, the two psalms are complementary.
For the music director; according to the alumoth-labben style; a psalm of David.
The meaning of “alumoth-labben” is uncertain. Suggestions include: “death of the son”, “secrets of the son” (LXX), “the youth of the son” (Aquila), “by female voices”, the name of a tune, or the style of singing.
1 I will thank the Lord with all my heart! I will tell about all your amazing deeds!
2 I will be happy and rejoice in you! I will sing praises to you, O sovereign One!
[The psalmist’s] intention to praise God issues not only from the knowledge and remembrance of such works in the past, but from anticipation of God’s deliverance from a specific situation and from a current experience. Yet it is the knowledge of God’s past works which provides understanding and hope in the current experience, and thus releases the desire to praise, as expressed here. 
3 When my enemies turn back, they trip and are defeated before you.
4 For you defended my just cause; from your throne you pronounced a just decision.
5 You terrified the nations with your battle cry; you destroyed the wicked; you permanently wiped out all memory of them.
6 The enemy’s cities have been reduced to permanent ruins; you destroyed their cities; all memory of the enemies has perished.
7 But the Lord rules forever; he reigns in a just manner.
God’s everlasting rule contrasts with the temporary threat of the wicked.
8 He judges the world fairly; he makes just legal decisions for the nations.
9 Consequently the Lord provides safety for the oppressed; he provides safety in times of trouble.
10 Your loyal followers trust in you, for you, Lord, do not abandon those who seek your help.
11 Sing praises to the Lord, who rules in Zion! Tell the nations what he has done!
12 For the one who takes revenge against murderers took notice of the oppressed; he did not overlook their cry for help 13 when they prayed: “Have mercy on me, Lord! See how I am oppressed by those who hate me, O one who can snatch me away from the gates of death!
14 Then I will tell about all your praiseworthy acts; in the gates of Daughter Zion I will rejoice because of your deliverance.”
The gates of Daughter Zion are the opposite of the gates of death in the preceding verse. They are characterized by righteousness and salvation .
15 The nations fell into the pit they had made; their feet were caught in the net they had hidden.
16 The Lord revealed himself; he accomplished justice; the wicked were ensnared by their own actions. (Higgaion. Selah)
Higgaion, like Selah, is a musical marker of some kind.
17 The wicked are turned back and sent to Sheol; this is the destiny of all the nations that ignore God, 18 for the needy are not permanently ignored, the hopes of the oppressed are not forever dashed.
The Hebrew literally says that the wicked will return to Sheol (the abode of the dead). It’s as if death is the natural state of the wicked. Goldingay takes the expression to mean the wicked will flee and perish.
19 Rise up, Lord! Don’t let men be defiant! May the nations be judged in your presence!
20 Terrify them, Lord! Let the nations know they are mere mortals! (Selah)
 Craigie 2004, p. 118
 Ps. 118:17-19
Craigie, Peter C., and Marvin E. Tate. Psalms 1-50. Nashville: Nelson Reference & Electronic, 2004.
Goldingay, John. Psalms: Volume 1: Psalms 1-41. Kindle Edition. Baker Academic, 2006.
Kidner, Derek. Psalms 1-72: An Introduction and Commentary. Downers Grove, Ill.: Inter-Varsity Press, 2008.
VanGemeren, Willem. Psalms. Grand Rapids, Mich.: Zondervan, 2008.