The three-volume novel (sometimes three-Decker or triple Decker) was a standard form of publishing for British fiction during the nineteenth century. It was a significant stage in the development of the modern Western novel as a form of popular literature.
The format does not correspond closely to what would now be considered a trilogy of novels. In a time when books were relatively expensive to print and bind, publishing longer works of fiction had a particular relationship to a reading public who borrowed books from commercial circulating libraries. A novel divided into three parts could create a demand (Part I whetting an appetite for Parts II and III). The income from Part I could also be used to pay for the printing costs of the later parts. Furthermore, a commercial librarian had three volumes earning their keep, rather than one. The particular style of mid-Victorian fiction, of a complicated plot reaching resolution by distribution of marriage partners and property in the final pages, was well adapted to the form.
Three volume novels began to be produced by the Edinburgh-based publisher Archibald Constable in the early 19th century. Constable was one of the most significant publishers of the 1820s and made a success of publishing expensive, three-volume editions of the works of Walter Scott, the first being Scott's historical novel Kenilworth, published in 1821. This continued until Constable's company collapsed in 1826 with large debts, bankrupting both him and Scott. As Constable's company collapsed, the publisher Henry Colburn quickly adopted the format. The number of three-volume novels he issued annually rose from six in 1825 to 30 in 1828 and 39 in 1829. Under Colburn's influence, the published novels adopted a standard format of three volumes in octavo, priced at 31 shillings and sixpence. The price and format remained unaltered for nearly 70 years, until 1894.
The standardized cost of a three volume novel was equivalent half the weekly income of a modest, middle-class household. And was enough to deter even comparatively well-off members of the public from buying them. Instead, they were borrowed from commercial circulating libraries, the most well known being owned by Charles Edward Mudie. Mudie was able to buy novels for stock at round half the retail price - five shilling per volume. He charged his subscribers one guinea (21 shillings) a year for the right to borrow one volume at a time. A subscriber who wished to borrow three volumes, in order to read the complete novel without having to make two additional trips to the library, had to pay a higher annual fee.