Like many showbusiness professionals, Shakespeare seems to have looked warily on people who thought they could do his job for the fun of it. His most famous depiction of am-dram is, of course, A Midsummer Night's Dream, where the "hard-handed men" of Athens stage their halting entertainment for Theseus and the lovers  a scene that lampoons, albeit gently, men "which never laboured in their minds till now" fancying themselves as playwrights and actors. Similarly, Love's Labour's Lost (perhaps written around the same time) culminates in a calamitous pageant put on by a schoolteacher and a curate, which fails to survive the former departing in a huff. Nor do directors manqués fare much better: Hamlet presumes to give the long-suffering players notes, and then dispatches them to perform a treasonous play in front of a murderous king. Equity, one imagines, would not be impressed.

In contrast to several of his colleagues, who wrote masques to be acted by well-bred amateurs at court, Shakespeare apparently resisted entrusting his scripts to untrained actors. The plays and poems repeatedly, even paranoically, tell us why: Sonnet 23 talks of "an unperfect actor upon the stage / Who with fear is put beside his part"; Coriolanus compares himself to a "dull actor" who can't remember his lines. Even Macbeth, surveying his dwindling life, finds his mind flickering back to the nightmarish idea that all along he has been an amateur, "a poor player / That struts and frets".

All of which makes it intriguing, as Michael Dobson's generous and fascinating study makes clear, that non-professional performers of all stripes have been so eager to follow Bottom, Holofernes and the rest into the unforgiving glare of the footlights. In the 17th and 18th centuries, aristocrats mounted private versions of the plays, elevating Shakespeare, so they saw it, from the clapper-clawing of the vulgar. At the other end of the social scale, the 20th-century Little Theatre movement  spearheaded by such groups as the Stockport Garrick Society  offered Shakespeare as a step on the ladder to working-class self-improvement.

Shakespeare and Amateur Performance makes a bold claim: that although performances in drawing rooms, private clubs and damp meadows have been neglected by theatre historians, they are as central to our Shakespearean inheritance as stagings at the Theatres Royal and the RSC. To an extent, this is persuasive. While it's common to regard Romeo and Juliet as the 18th century's favourite play, for instance, it's interesting to hear that it was avoided by amateurs, seemingly on the basis that it would incite biddable young people to flout their parents (or, worse, young ladies to flash their calves). And though it is usually assumed that Hamlet was first acted at the Globe, in fact the earliest performances on record were non-professional  aboard, of all places, a East India Company galleon anchored off Sierra Leone in 1607, in front of a west African king. The event indicates not just the play's apparent portability; it shows, as Gary Taylor has argued, Shakespeare becoming a commodity in England's expanding empire.

Although the book struggles to make a consistent case about non-professional performance  partly, one suspects, because of patchy evidence  that is perhaps the point. Dobson continually reminds us that Shakespeare, far from being a stable ontological entity, is almost unrecognisably different in different contexts. To someone like Sir Edward Dering, who staged a conflation of the Henry IV plays at his country house at Surrenden, Kent in 1623 (more well known as the year that the First Folio was published), Shakespeare was a chronicler of political intrigue, usefully echoing the mounting crisis at court. To the Harris family, who put on an all-female adaptation of The Winter's Tale at their Salisbury residence in 1774, he was a dramatist unusually sympathetic to women, not least because the play allowed them to demonstrate an eye for fine costume. (Excitement at dressing-up is one constant of amateur performance; Bottom's enthusiasm for fake beards clearly leads the way.)

Dobson is particularly engaging on the history of military Shakespeare. During the American war of independence the Bard was fighting on opposing sides  British troops commandeered theatres in Philadelphia then New York for plays by "Old Shakespeare" while the rebels put on Coriolanus at Portsmouth, New Hampshire. Seventy years later, a young Ulysses S Grant would play Desdemona in a US Army Othello, a play that has always had great resonance for soldiers (a fellow actor complained that he "did not have much sentiment"). Some military performances raise more agonising ideological questions: were allied prisoners of war who performed Shakespeare in internment camps striking a blow for intellectual freedom, or playing along with their Nazi captors, who enthusiastically provided costumes and makeup? The issue is given point by the fact that one group of prisoners acted The Merchant of Venice without knowing that Dachau was only 50 miles away.

Among the book's insights is that the line between "amateur" and "professional" has always been blurred. Many professionals support their theatrical careers by working in other industries, and am-dram itself has nurtured many a thesp  notably Ian McKellen, now patron of Bolton Little Theatre, where he first performed as a boy. Via the late-20th century craze for outdoor performance, it has brought hundreds of thousands of people into contact with live Shakespeare; indeed, Dobson balefully notes, "from June to August it is still practically impossible to be more than 20 miles from an open-air Shakespearean venue . . . without fleeing to the moorlands of Scotland".

Occasionally am-dram has led the way. In the 1880s, while professional producers were creating ever more ponderous pictorial stagings, the visionary director William Poel tried out with volunteers what would have been impossible with professionals  a neo-Elizabethan Hamlet, the first attempt at "authentic" performance. Along with Nugent Monck's pioneering amateur Maddermarket Theatre in the 1920s, it helped restore the virtues of Shakespeare's fluid, fast-paced theatre to the theatre of our own time. Amateurs may well be doing it for the love of it (the word comes from the Latin amare), but sometimes all of us are in their debt.

Andrew Dickson's Rough Guide to Shakespeare is published by Penguin.