It is startling to realise, on the 400th anniversary of John Milton's birth, currently celebrated by an exhibition at the Bodleian Library, that many of his ideas are still the subject of hot political debate.

Some - abolition of the monarchy and disestablishment of the Church, for instance - seem alarmingly radical even in 2008.

Citizen Milton is a breathtaking display of manuscripts, printed books and art, mostly taken from the Bodleian's very extensive holdings relating to the poet.

It is supplemented by other wonderful items, such as Samuel Palmer's watercolour The Prospect - inspired by Milton's early poem L'Allegro - which is on loan from the Ashmolean Museum, and, from Keble College, a first edition of Paradise Lost. (The ending in this copy has been re-written by a reader to make it a bit more upbeat!) The exhibition, put together by Sharon Achinstein, a Milton scholar and Fellow of St Edmund Hall, sets out to demonstrate through the detail of the poet's life and writing, and through the work of those influenced by his thinking in later centuries, the modern relevance of his concept of the virtuous citizen', acting on the side of right, for society as a whole.

Together with this went a passionate belief in the importance of education for a truly democratic society, and the defeat of tyranny and intolerance of all kinds, particularly where it involved religious matters and the freedom of the press.

In Areopagitica (1644) he wrote: As good almost kill a man as kill a good book' responding to Parliament's attempt to censor his Doctrine and Discipline of Divorce, whose contents it had condemned as licentious, new and dangerous'.

Both these important works feature in the exhibition - Areopagitica has been much reprinted since, whenever censorship has threatened to reappear.

The Bodleian is a nicely appropriate venue. Though he studied as a young man at Christ's College, Cambridge, Milton later had a friendly, and mutually helpful, relationship with Bodley's Library and its brave and principled librarian, John Rouse.

He considered the library vital to the causes of liberty and free speech which he espoused, and donated several of his own books, including the sensational and widely read Pro Populo Anglicano Defensio (Defence of the English People), published in 1651, editions of which can be seen here.

In 1660, with the restoration of Charles II, this treatise justifying the execution of Charles I was condemned by the new government to a bonfire in the quad, along with other republican tracts by then considered seditious. On this occasion, and again in 1683, the Bodleian saved Milton's work from the flames. A copy of the proclamation demanding its destruction is on display, alongside an under-the-counter list noting that Areopagitica and Milton's volume on divorce had actually been purchased for the collection but were not to appear in the official catalogue. As well as working on commissions from the Commonwealth Parliament's Council of State for revolutionary writing such as Pro Populo, Milton acted as its Secretary to Foreign Tongues, using his Latin to help with diplomatic correspondence.

His sight was already failing, which made him all the more determined to contribute what he could to the success of the cause before the onset of total blindness. The poet Andrew Marvell, who had become a friend, served as his assistant.

Visitors to the exhibition can see one of Milton's letters to Queen Christina of Sweden, who embodied many of his ideas of what a good Royal should be, not least by eventually abdicating! Also from this period are a sonnet To Oliver Cromwell' and a manual of Elizabethan statecraft, published by Milton and said to be written by Sir Walter Raleigh.

From the failure of the Commonwealth until his death in 1674, Milton and his ideals were the subject of much monarchist ridicule - the despair he felt at this time is powerfully expressed in the woodcut by A Garth Jones for an 1898 edition of Milton's 1671 poem Samson Agonistes.

As the exhibition shows, the poet has inspired a great deal of visual material, particularly book illustration, over the last 400 years. A hand-coloured etching from Blake's 1790 Marriage of Heaven and Hell, for example, daringly suggests an interpretation of Satan as the true hero of Paradise Lost, an idea taken up by several contemporaries of Blake's whose work appears here.

There are also examples of the way in which Milton's revelation of a whole new universe of political, artistic and literary possibility influenced the left-leaning private presses of the Arts and Crafts Movement.

These include a 1931 edition of Milton's masque Comus, produced by the Gregynog Press, and the 1905 Paradise Regained from Doves Press. A new, extremely simple, typeface was designed for this book, to complement the magnificence of the text, and, in a dramatic gesture towards the artistic integrity so important to the Movement (and to Milton), thrown into the Thames a few years later so that it could not be re-used.

The appreciation of Milton's work outside England is represented by several translations of Paradise Lost into French and German. There's also a 1918 Russian melodrama Oliver Kromvel by one Anatoly Lunacharsky, The People's Commissar of the Enlightenment. Milton features among the dramatis personae of this play, which attempts to relate the ideals of the Commonwealth to those of the Russian revolution.

Modern authors who have explored some of Milton's themes also find a place in the exhibition; for instance Philip Pullman's His Dark Materials, Tony Harrison's poem On not being Milton and Geoffrey Hill's A Treatise of Civil Power. Illustrations of Paradise Lost by Terence Lindell for Heavy Metal magazine in 1980 exemplify his influence on 20th-century popular culture.

The events of Milton's domestic life, while not the main focus of the display, are touched on. His horoscope is here, as is a grisly account of the poet's rather shocking disinterment in 1790, at which a number of bodily relics were salvaged for posterity, including locks of his hair which passed into the possession of admirers such as Keats and Leigh Hunt.

This is an extraordinary opportunity to see some fantastic things - work of huge political, literary and artistic importance - and to join in the celebration of Milton's great legacy to the world. Make the most of it!

Citizen Milton runs until April 26 in the Bodleian's Exhibition Room, Old Schools Quadrangle. Open Monday-Friday 9am-5pm, Sat 9am-4.30pm. Admission free. Visit the online exhibition at: www.cems.ox.ac.uk/citizenmilton