Giovanni Boccaccio is, with the older Dante and his contemporary Francis Petrarch, one of the three great poets of the Italian fourteenth century. Chaucer knew the works of all three, and it has been speculated that he may even have met both Petrarch and Boccaccio (but see below).
Of the three, Boccaccio was the one on whom Chaucer drew most heavily, and in some sense strove to emulate; Chaucer based Troilus on Boccaccio's Il Filostrato and his Knight's Tale on Il Teseida, and Chaucer's elaborate high style owes something to Boccaccio's attempt to emulate the classics in his own vernacular. In his Monk's Tale, Chaucer drew on Boccaccio's Latin works, his account of the falls of famous men and his book of illustrious women. A number of the Canterbury tales tell stories that also appear in Boccaccio's Decameron.
There is a slim possibility that Chaucer met Boccaccio, who was living in Certaldo, just south of Florence, in the 1370s, when Chaucer was in Italy. Donald Howard, in his biography (Chaucer: His Life, His Works, His World. New York. 1987 [PR 1905.H58 1987]), speculates that the two did indeed meet in Certaldo; Derek Pearsall (The Life of Geoffrey Chaucer, A Critical Biography. Cambridge, MA. 1992 [PR 1905.P43 1992]) is more cautious.
Chaucer must have known about the Decameron, though there is no proof of this, since he never quotes it directly. Most likely, he knew the work, had even read it, but did not own a copy. Yet comparing Chaucer's and Boccaccio's treatments of the same traditional stories yields interesting contrasts in their views of literature and of the world.
For a complete e-text of the Decameron, see the Decameron site at Brown University, a fascinating site, well worth exploring.
The following tales have analogues in Boccaccio's Decameron:
Franklin's Tale: Day 10, Tale 5
Merchant's Tale: Day 7, Tale 9
Pardoner's Prologue: Day 6, Tale 10
Not an analogue, but interesting for its contrast to the General Prologue, is the introduction to the Decameron, with its chilling account of the Plague in 1348:
Decameron: Day 1, Introduction
The Preface and Conclusion are interesting for the audience they define and for the defense of indecorous stories, somewhat similar to that which Chaucer offers in the General Prologue.
For a printed English translation see: The Decameron of Giovanni Boccaccio, tr. Richard Aldington, any printing [PQ 4272.E5].
For the source of the Knight's Tale:
Chaucer's Boccaccio: Sources of the Troilus and the Knight's and Franklin's Tales, ed. and tr. N.R. Havely. Woodbridge and Totawa. 1980. [PR 1912.B6 1980].
The Book of Theseus = Teseida delle nozze d'Emilia by Giovanni Boccaccio, tr. Bernadette Marie McCoy. New York. 1974 [PQ 4722.E5 T4 1974]. The introduction (pp. 3-9) contains a helpful summary of the work.
A possible source of the Franklin's Tale:
Il Filocolo, tr. Donald Cheny with the collaboration of Thomas Bergin. New York. 1985 [PQ 4272.E5 F4 1985].
Thirteen Most Pleasant and Delectable Questions of Love, Entitled a Disport of Diverse Noble Personages. Written in Italian by Giovani Boccaccio in his book Filocolo. First turned into English by H.G. in 1566 and now refashioned and illustrated by Harry Carter. [PQ 4272.E5 F4 1974].
The source of Troilus:
The Story of Troilus [= Il Filostrato], tr. R.K. Gordon. New York. 1964 [PN 6071.T76 G67 x, 1964]. Useful because it contains other versions of the story (Benoit's Old French version and Henryson's "continuation"). However, the new edition of Troilus and Criseyde by Stephen A. Barney, a Norton Critical Edition, is far superior to this and to Rosetti's edition (Chaucer's Troylus and Criseyde (from the Harl. ms. 3943), compared with Boccaccio's Filostrato, tr. Wm. Michael Rosetti. EETS 44, 65. London. 1873-83 [Widener: 11482.44]). Useful because it prints the texts in parallel, but Barney's better Norton edition is to be preferred.
See also Havely's translation above.
The sources (in part) of The Monk's Tale:
Concerning Famous Women [De mulieribus claris], ed. and tr. Virginia Brown. Cambridge, MA. 2001 [PR 4274.D5 E.5 2001].
Die mittelenglische umdichtung von Boccaccio's De claris mulieribus [Middle English trans. of De mulieribus claris], ed. Gustav Schliech. Leipzig. 1924. [PQ 4274.D5 E5 x, 1924].
The Fates of Illustrious Men [De casibus virorum ilustrium], tr. and abridged by Louis Brewer Hall. New York. 1965. [Widener: Ital 7185.22]
Lydgate's Fall of Princes [Middle English trans. of De casibus virorum illustrium], ed. Henry Bergen. EETS, 121-24. London. 1924-27 [Widener: 11472.121].
Of General Interest:
Giovanni Boccaccio, In Defense of Poetry [Genealogie deorum gentilium liber xv], ed. from Univ. of Chicago MS. 100 by Jeremiah Riedy. Toronto. 1978 [Widener: ML 20.5 vol.8].