Take Martin Amis's The Rachel Papers. Although it was published as recently as 1973, first editions are already selling in specialist bookshops for pounds 400 - but only if in excellent condition, with a pristine dust-jacket.
First editions of successful authors' books are increasingly popular - and the market is developing to include paperbacks.
You will know if you have a first edition, because it will normally say inside "first published" or, sometimes, "first printing" - and nothing more. US first editions may even say "first edition".
A first edition signed by the author, particularly if dedicated to a loved one, will boost the price. "Dying helps," says Simon Roberts, deputy head of the books department at Phillips auctioneers. The going rate for Graham Greene novels shot up after he died, and the same may now apply to the work of Ellis Peters, who wrote the tales about the detective monk Cadfael and who died last weekend. And Seamus Heaney's Nobel Prize should be good for the selling-price of his earliest work.
Rarity is another key to price. Authors' early books usually sell for the highest prices, because they had the smallest print runs. Anyone who recognised Ian Fleming's Casino Royale as a masterpiece of its genre, and wrapped it up to keep it in mint condition, could now sell it for pounds 2,000. A first edition of Phillip Larkin's XX Poems, of which only 200 were printed, could fetch a similar amount.
But prices drift as fashions change. The Rachel Papers ceased rising in value a year ago; Mervyn Peake's Gormenghast Gothic trilogy, cult books 20 years ago, sell for little more now than they did then; and copies of D M Thomas's The White Hotel, in great demand a few years ago, are virtually worthless now.
Anthony Rota, director of Bertram Rota, specialists in 19th-century and 20th-century British and American books, says that collectors who are investing should buy only authors who will endure. "Don't take the fast risers. Look for a solid body of work," he advises.
The fast risers in the past few years have been a select band of male, white British authors: Martin Amis, Ian McEwan, William Boyd, Graham Swift, and Julian Barnes, whose first editions outprice literary classics. Over the longer term, strongest demand has been for the work of such important literary figures as TS Eliot and James Joyce. A signed first edition of Ulysses can realise pounds 25,000.
But Marie-Helene Oliver of Christie's says: "Contemporary authors are worth collecting now. Put them away in a cupboard." The Christie's November sale will include Ian Fleming and Katherine Mansfield first editions.
Bestsellers are as worth collecting for investment as are potential classics - early Dick Francis books sell well, an example of his first book, Dead Cert, recently selling for pounds 500.
Ms Oliver advises new buyers to visit collections, such as those in some libraries, to examine good-quality first editions before making a purchase. It can otherwise be difficult to rate condition. Some dealers worry that because books with mint-condition dust-jackets can fetch up to eight times as much as those without them, unscrupulous sellers may produce fake covers using high-quality colour copiers.
Peter Ellis, part-owner of the Ulysses bookshops, has one shop devoted to first editions. He says experienced collectors will not be fooled by photocopied jackets. "I have not heard of anybody sold a fake as a real one."
The enthusiastic collector who wants to take a long-shot punt may do well collecting from new, but another option is to trawl second-hand bookshops, armed with a copy of the secondhand bookseller's bible, Modern First Editions by Joseph Connolly (Little, Brown & Co.).
Malcolm Hornsby runs a bookshop in Loughborough, where first editions often pass through his hands. He advises caution: "First editions go down as well as up, and they have waves. The rising stars of 20 years ago are in some cases diminishing in value, and you can't get the same money for them. It's an inflated market, and some books are going for huge prices, and books which once cost a fortune you can't give away now.
"I am laying by signed copies of Margaret Atwood novels, which will be looked at in 20 years the same way as Angela Carter is now. You can buy your first editions through collectors or specialist dealers and pay the top price, and you can get what you want. But every secondhand bookseller has books which are not on display, because of the risk of being fingered, so ask."
First editions under the hammer
Sotheby's of New Bond Street, London W1 (0171-493 8080), has frequent sales of first editions; the next is on 9 November. Christie's of Old Brompton Road, London SW7 (0171-581 7611), holds two sales of first editions a year, with the next on 17 November. At Phillips of New Bond Street (0171- 629 6602), monthly general sales usually contain first editions; the next is on 9 December. Bonhams of Montpelier Street, London SW7 (0171-584 9161), holds five sales a year of first editions; the next is on 31 January. Ulysses booksellers of Museum Street, London WC1 (0171-831 1600), and Bertram Rota of Langley Court, Covent Garden WC2 (0171-836 0723), specialise in first editions.