One word – bibliomania – seems to sum up the great private libraries of the late eighteenth and early nineteenth centuries. The word was already being used in England as early as 1734, when Thomas Hearne commented on the low prices fetched by the manuscripts at the sale of Thomas Rawlinson’s library – ‘had I been in place I should have been tempted to have laid out a pretty deal of money, without thinking myself at all touched with Bibliomania’ – but it is more commonly associated with the early nineteenth century, the period celebrated in Thomas Frognall Dibdin’s Bibliomania (1811), when the prices of rare books in England rose to unprecedented heights. It has been succinctly and accurately defined by Marc Vaulbert de Chantilly as ‘the rage for rare, curious and splendid books which gripped a number of wealthy, well-educated and well-born Englishmen over a period of approximately fifty years’, between about 1775 and 1825. Like the Dutch ‘tulipomania’ of the late seventeenth century, the English bibliomania of the early nineteenth century has often been seen as a brief and exceptional period of unbridled extravagance, when books were bought and sold at prices far exceeding their intrinsic value. There is certainly a good deal of truth in this view; but as I hope to show in this chapter, the era of bibliomania was not merely a blip in the history of English book-collecting. On the contrary, it represents a profound shift in literary taste, and has had an equally profound and enduring impact on the collecting of books and the formation of libraries.