If you are the proud owner of a first edition of J.K. Rowling's Harry Potter and the Philosopher's Stone, then you are in luck. The book, which first came out in 1997, is worth an estimated GBP10,000 (HK$127,000) to GBP12,000, which is a fair amount more than the few hundred dollars you probably spent on it. This is just one example of many titles that have increased in value over the past decade thanks to a growing market for collectable books. While the trade is already well established in Europe and America, it's taking off in Asia thanks to the internet. And now that Hong Kong hosts the annual International Antiquarian Book Fair, numbers here are set to grow. 'The internet and e-commerce has completely changed the rare book industry in the past 15 years. It means that books can be found or researched easily on the internet,' says Jonathan Wattis, owner of Wattis Fine Art, which specialises in historical books about Hong Kong and Southeast Asia. 'There was always a community of people interested in buying but there was nowhere to go to. Now that the taps have been turned on for supply, there's more demand,' says Christopher Bailey, owner of Picture This Gallery. Book collecting carries broad appeal because it covers many subjects. At Lok Man Rare Books, which opened five years ago, owner Lorence Johnston stocks more than 1,000 titles covering topics such as recipes and cocktail-making to poetry, children's books and travel. An avid reader, he opened the store because he wanted to offer gifts not found elsewhere. For Dr Peter Kennedy, a professor at University of Hong Kong, book collecting is a passion that began at age 12. 'I was aware of the importance of books and reading from early on,' he says. 'It was also the beauty of books themselves that I loved - the sensual pleasure, smell of them, thrill of sending off for books and unpacking them when they arrive,' he adds. Rare or collectable books fall into two categories, antiquarian and modern. Modern books were printed after the early 1900s (or to be exact, after 1920, according to Johnston) while anything antiquarian is pre-1900. Age is just one factor affecting price, along with condition, rarity and beauty. 'Condition is probably the most important factor when buying an antique book. I would advise you to buy the best condition possible that fits within your budget. For modern books, it means buying them with the dust jacket intact. A jacket can account for up to 95 per cent of the value of the book,' says Johnston. Also coveted are first and signed editions, although it very much depends on who the author is. 'First editions are usually the most special, unless the second edition has special features such as extra information or illustrations,' Wattis says. 'One of the most expensive books ever sold is an atlas by Greek scholar Ptolemy that features incredible illustrations that are hand-coloured.' While some collectors go for subject matter or author, others tend to buy books purely as works of art. In addition to illustrations, unique bindings by private presses such as Golden Cockerel (1920-1961) or Chelsea Bindery transform old editions into objects of beauty. The Chelsea Bindery, for example, has released a leather bound first edition of Breakfast at Tiffany's featuring a silhouette of Audrey Hepburn with real diamonds decorating her tiara and neck. Most experts tend to brush aside the investment potential of rare books. But others do invest. 'Some people are buying books as investments, there is no doubt. Books generally plod along at a fairly good level and keep their value, especially if they are kept in a good condition,' says Wattis, pointing to a second edition of Narrative of the Voyages of the Nemesis from 1840 to 1843 that he bought seven years ago for GBP500 to GBP600. It is now worth more than GBP1,200. 'There are those that do well in the short-term market because there are always trends, like Harry Potter, for example. But if you look forward 50 years I don't know how it would rate if you put them alongside Darwin or Shakespeare. It's like fashion and changes all the time,' he says. As with stocks, a book's monetary value can be affected by factors such as the economy, market trends, timing and, of course, luck. 'Some books go up faster than others, while some go out of fashion and actually go down. It's like stocks,' Bailey says. 'Photography books about China in the 1920s have gone up in multiples but I can't tell you what the trend is going to be in 20 years.' Nevertheless, there are some notable trends taking root in the local market. Johnston is amassing a collection of rare wine books since wine collecting is popular, while Wattis and Bailey point to Chinese photography books and historical travel books thanks to an influx of buyers from the mainland. Classic authors such as Ernest Hemingway, Ian Fleming and Charles Dickens are always popular, although you should plan to fork out big bucks. If you are searching by subject, then everything China-related is booming. 'Chinese art books are very popular at the moment because of the interest in art and because they are hard to find,' Bailey adds. Experts tend to emphasise the personal and cultural value of books over their monetary value. 'For me, it's madness. I often use the investment thing as an excuse to buy more books but it's just a justification, as I will never sell them. If anything I will donate them to a university or society,' Kennedy says. Tome is money US$30.8 million Leonardo da Vinci's Codex Leicester, 1994, Christie's. Da Vinci's notes about the link between art and science are illustrated with his drawings and sketches. It is the most expensive book ever. Bill Gates bought it in the 1994 auction. US$21.3 million Magna Carta, 2007, Sotheby's. A manuscript of the 'Great Charter' was first issued in 1215 to define people's individual rights and freedoms under English law. Sold by the Perot Foundation. US$13.4 million Rothschild Prayerbook, 1999, Christie's. The Rothschild Prayerbook is an illuminated manuscript book of hours, illuminated over the period 1500-1520 by artists in the Flemish region of modern-day Belgium. US$12 million Gospels of Henry the Lion, 1983, Sotheby's. Estimated to have been produced around 1188, it includes four gospels and 50 miniature paintings that document Henry's quest for power. US$11.5 million John James Audubon's Birds of America, 2011, Sotheby's. The auction price is the most fetched for any printed book. With more than 400 paintings of different species, Audubon used these illustrations to create engraved plates that were sold between 1827 and 1838.