William Langland seems to have kept re-writing the same alliterative poem again and again, so we have an "A text" (from before 1376), a "B text" (from 1378), and a "C text" (from about 1387). It is considered a "monumental work of social consciousness of the 14th century, earnest in its satire, realistic in its humor" (Garbáty 676).
The control Langland has over the poem is questionable, the narrator going in and out of dream visions but also going into a dream within a dream and ultimately not coming out enough levels. But the poem does have one of the best depictions of the procession of the Seven Deadly Sins.
Langland, William. The Vision of Piers Plowman: A Complete Edition of the B-Text. Ed. A.V.C. Schmidt. London: J.M. Dent and Sons, Ltd., 1978.
Piers Plowman. Medieval English Literature. Ed. Thomas J. Garbáty. Lexington, Massachusetts: D.H. Heath & Co., 1984. 676-720.
Piers Plowman. The Norton Anthology of English Literature, Volume 1. 8th ed. NY: W.W. Norton & Co., 2006. 331-367.