It's a tough call for my book of the year - either Oxford's Companion to the Book or Stephen Sondheim's Finishing the Hat. Both encapsulate an entire art form and both sit on my table like a never-ending box of ginger chocolates, infinitely dippable. The Companion tells you everything you never dreamed of asking about the precious object that contains all human knowledge and, we keep getting told, is about to disappear. Finishing the Hat shows the workings of the stage musical, soup to nuts, by a composer who, according to cliché, has written its epitaph. Both have laugh-out-loud moments: the Companion on the origins of the dirty book and Sondheim on the prissiness of Noel Coward. Go on, treat yourself. You'll never find such fun and wisdom on Wikipedia.