Psalms 117:1-2
1 O praise the LORD, all ye nations: praise him, all ye people.
2 For his merciful kindness is great toward us: and the truth of the LORD endureth for ever. Praise ye the LORD.
The shortest chapter in the Bible, and the middle chapter. It is a doxology, calling all peoples to praise Jehovah. It may have been appended to some Ps.