1
general::
Phrase(s): again and again
repeatedly; again and even more [times]. • He knocked on the door again and again until I finally answered.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Repeatedly, often, as in I've told you again and again, don't turn up the heat. This idiom uses repetition for the purpose of emphasis (as does its synonym, OVER AND OVER). Shakespeare used it in Othello (1:3): "I have told thee often, and I retell thee again and again." [c. 1600]
American Heritage Idioms