A play generally accepted as having been written by William Shakespeare around 1594 or 1595. It first appeared in print in 1597. Even before the Shakespeare play though, this story of two "star-crossed lovers" was widely popular in Europe. It is said that Shakespeare borrowed much of his artistic rendering of the tale from a poem by Arthur Brooke entitled The Tragical History of Romeus and Juliet. Brooke in turn based his poem on the works of writers previous to him. Here's an excerpt from an essay by David P. Stone which describes, in brief, the evolution of the Romeo and Juliet story:
The story was popular, on the Continent at least, before Elizabeth's time. The first version was that which appeared in Salernitano's 'II Novellino' in 1476. This version had the clandestine lovers, the accommodating Friar, the killing that led to the young man's banishment, the rival suitor, the sleeping potion, thwarted messenger, an unhappy conclusion; but no suicides. This might have passed into oblivion had it not been for Luigi da Porto's "Istoria novellomente ritrovata di dui Nobili Amanti", published about 1550, which laid the scene in Verona and identified the families as Montecchi and Capelletti. Da Porto's story also named the friar as Lorenzo and the slain man as Thebaldo Capelletti and introduced the ball, the balcony scene and the double deaths inside the tomb. It was da Porto who first named the minor character Marcuccio and gave him the icy hands which subsequent tellers of the tale mention in great detail but which Shakespeare disregarded in favour of a definite character. Da Porto is also remembered for having Juliet commit suicide by holding her breath - a detail which no one, fortunately, bothered to perpetuate.
Da Porto's tale was widely imitated both in Italy and France, but the version of most importance to readers of Shakespeare was that of Mateo Bandello, who put the story into his "Novelle" of 1554. Of all the versions before Shakespeare's, Bandello's is generally considered to be the best. It is plain, straightforward narrative, unmarred by the sentimentality and moralising that characterised the work of some of his adapters. In Bandello's story the masking is there, the servant Peter appears -but as Romeo's man- the Nurse has a significant part in the plot, the rope ladder comes into play and the theme, as we now have it, takes on more of a definite shape.
Almost as important as the Bandello version is the one adapted from it by Peirre Boaisteau in 1559 which was included in Bellforest's 'Histories Tragique'. Boaisteau made Romeo go to the ball in the hope of seeing his indifferent lady, Rosaline; worked out the business of Lord Capulet's restraint at discovering Romeo's presence and developed the dilemma in which Juliet finds herself when she learns of Tybalt's death at the hand of her husband. He also developed the character of the apothecary.
All of these contributions went into Painter's version which was presented in 1567. This was a translation of Boaisteau's version and from this was derived Arthur Brooke's poem. So the plot sources of the play are: Salernitano, da Porto, Boaisteau, through Painter's translation to Brooke, in that order. Of these, Shakespeare used only Brooke directly and thus derived from the tradition only that which Brooke had left him. But he borrowed freely from the great wealth of detail which Brooke himself had offered. - http://members.tripod.co.uk/scorpius/index.htm
Shakespeare's version in its entirety is noded below by scene. For a neato synopsis of the play, see Shakespeare : Romeo and Juliet.
The Most Excellent and Lamentable Tragedy of Romeo and Juliet
by William Shakespeare
CHORUS - Prologues
MONTAGUE - his father
LADY MONTAGUE - his mother
BENVOLIO - nephew to Montague, friend to Romeo
BALTHASAR - Romeo's man
ABRAHAM - servant to the Montagues
CAPULET - her father
LADY CAPULET - her mother
NURSE - nurse to Juliet
TYBALT - nephew to Lady Capulet
PETER - servant to the Capulets
SAMPSON - servant to the Capulets
GREGORY - servant to the Capulets
PRINCE Escalus - prince of Verona
MERCUTIO - his kinsman, friend to Romeo
County PARIS - young nobleman, kinsman to the prince
PAGE to Paris
Various Franciscans, Watchmen, Guards, Masquers, Guests, Musicians, Citizens and Attendants
SCENE - Verona; Mantua
Prologue and Scene I
Prologue and Scene I