Any thorough investigation or study of Marlowe and his works inevitably turns up the theory that Marlowe wrote some or all of the works of William Shakespeare. The most extreme form of the argument is that Marlowe's death was faked, presumably because of his secret government service, and that Marlowe left England after 1593 and continued to write plays for the stage whilst in exile. It is most often suggested that Marlowe lived in Italy, because so many of Shakespeare's later plays take place in that country. While there is no definite evidence to give weight to this theory, the strange lack of evidence about Marlowe's death, and the fact that the Elizabethan espionage community (with which Marlowe was involved) had been known to fake deaths and create new identities for agents makes it a somewhat plausible idea. Some authors contend that there is no way to prove Marlowe lived beyond 1593 (Nicholl 344,) and others, equally respected, conclude that the holes in the information about Marlowe's death and posthumous textual evidence in the plays of Shakespeare point directly to that very possibility (Michell 250). That said, at this time there is no irrefutable evidence -- and considerable evidence to the contrary -- that Marlowe either survived the attack in Deptford, or that the attack was faked, or that someone died in his place.
The main Marlovian theorists cite extensively from Shakespeare's later works, comparing them in style and content to Marlowe's. But an inherent flaw is contained in this exercise. The idea of intellectual property, or copyright, was in its infancy in Elizabethan times, and was considerably much more flexible than it is today. Marlowe himself lifted entire blocks of verse from other published plays and inserted them into his own plays. He then went on to publish these plays, claiming them as entirely his own and offering no citation for what we would consider plagiarized content contained in his work. This was common and accepted in Marlowe's day, and not considered dishonest or shoddy writing practice. Therefore, it is easily within the realm of possibility that Shakespeare, writing presumably before and after Marlowe's death in 1593 (none of Shakespeare's plays were published before that date) would have borrowed from what he knew of Marlowe's work, and copied his style freely. There are also many theories about the authorship of Shakespeare that do not include Marlowe, but up to thirty-six other plausible candidates (singly or as groups – Michell 243.)
Along the continuum of Shakespearean and Marlovian literary criticism and theory there are more moderate practitioners who see a great deal of collaboration between Shakespeare and Marlowe before the latter's death. The world of London theatre was at that time very small, and although there was no evidence that Shakespeare and Marlowe ever met each other (Michell 227,) it is nevertheless extremely likely. Both writers were in London at the same time, the practice of collaboration and borrowing between writers was well-established and expected, and it is, in the very least, doubtless that Shakespeare's blank verse in his early plays "bears the stamp of Marlowe's inspiration" (Michell quoting Sir Sidney Lee, Ibid.) It is generally accepted even among the most conservative Shakespearean scholars that Marlowe had some input in the early plays Titus Andronicus, Richard II, Richard III, and the three parts of Henry VI (Ibid.)
Several books and articles – some of them by respected Elizabethan literature scholars – have been written claiming Marlowe wrote most or even the entirety of Shakespeare's oeuvre. The idea is romantic and interesting, but, beyond some heavy borrowing and some quite predictable and expected collaboration between the two contemporary playwrights, no real evidence has been found for a direct one-for-one Marlowe-for-Shakespeare substitution. Textual comparison between the two playwrights' works is fraught with possible errors, as not only wholesale borrowing and copying was practiced in the Elizabethan theatre, but later copyists and editors of the four-hundred-year-old works changed the texts to such an extent that any kind of "pure" analysis was rendered impossible (Michell 229). There is evidence that Shakespeare's work was written by many hands other than Marlowe's. While the textual evidence is intriguing and sometimes very convincing (such as the Touchstone scenes with Audrey and William in As You Like It Act V, Scene I in which Touchstone (here presumed to stand for Marlowe) says to William (the character representing William Shakespeare) :
"Then learn this of me: to have is to have; for it is a figure in rhetoric that drink, being poured out of a cup into a glass, by filling the one doth empty the other, for all your writers do consent that ipse is he: now you are not ipse, for I am he."
As intriguing as it is, there is, at this point, no way of pinning Shakespeare's plays on Marlowe or any other author with any kind of surety. While the influence and collaboration between the two can be easily believed, anything beyond that is extremely difficult, if not impossible to prove four hundred years after the fact. Perhaps our modern difficulties lie more in our steadfast belief in single-authorship as a necessity of great literature. Elizabethan theatre was more collaborative and less concerned with protecting "intellectual property" than our contentious, litigious age, and so it may be that the great Shakespeare Authorship question has less to do with the events in the late 16th and early 17th century than it does with our own modern predilections for the preeminence of individual achievement.