For a general introduction to the place of Piers Plowman in literary tradition you may usefully consult the following online resources:
The Luminarium website on William Langland.

The Wikipedia entries for Piers Plowman and William Langland are for the most part quite trustworthy.

John Matthews Manly's chapter on '"Piers Plowman" and its Sequence' in  The End of the Middle Ages, vol. 2 in the Cambridge History of English Literature (1907-27), though a century old and out of line with modern views regarding authorship, still contains lots of useful information about the poems, their contexts, and their legacy.

The Introduction to Knott and Fowler's edition of the A Version may also prove useful.

(7 January 2008)