The words are by Saint Thomas Aquinas. It has been set to many different musical compositions. Most popular seems to be Caesar Franck's version.
Panis angelicus
Fit panis hominum:
Dat Panis coelicus
Figuris terminum:
O res mirabilis!
Manducat Dominum
Pauper, servus et humilis.
Lo! the Angelic Bread
Feedeth the sons of men:
Figures and types are fled
Never to come again.
O what a wondrous thing!
Lowly and poor are fed,
Banqueting on their Lord and King.