The folios are known as Comedies, Histories and Tragedies

A couple of actors in Shakespeare's company - John Heminges and Henry Condell - decided to publish the works in honour of the playwright.

A preface to the collection says it is "without ambition either of self-profit or fame, only to keep the memory of so worthy a friend and fellow alive as was our Shakespeare".

The Tempest, Taming of the Shrew, Twelfth Night, Coriolanus, Julius Caesar and Macbeth are included in the collection, grouped by theme.

Among its previous owners are the descendants of the poet John Dryden.

The Second Folio dates from 1632 and comes from the early 18th Century collection of the Earls of Aylesbury.

Julius Caesar: Shakespeare's works appear in myriad forms

The value of this work is put at around $150,000 (�102,000).

The 1664 Third Folio is a copy of an earlier work in a contemporary binding and that is expected to fetch around $200,000 (�136,000).

And the Fourth Folio, estimated at $300,000 (�204,500), is said to be the finest copy in existence and bound in gold-tooled black goatskin.

All of the works are part of the collection of a Chicago based book collector, Abel E Berland.

Some 500 titles from Romantic poetry to scientific texts will go under the hammer in New York on 8 and 9 October.

The Shakespeare folios are considered to be "the heart" of the collection, which Berland had always envisaged selling to the next generation.

"I never take them (my books) for granted," Berland remarked in an interview.

"I am nothing more than their temporary custodian."