Possibly as early as the late 1600's, when books were still expensive enough that the even wealthy people could not afford to buy very many books, yet no longer the impossibly expensive, hand-illuminated volumes of ages past, the fairly well to do person embraced the idea of borrowing books for a nominal fee from a circulating library. During the mid 1700's, as a growing number of people bought subscriptions to circulating libraries, they became profitable enough that more libraries cropped up, gaining wide popularity among the wealthy and growing middle class alike. Prior to that, subscription libraries and social libraries did exist but they typically offered a limited number of books and periodicals to their select group of members. Circulating libraries offered a huge range of interests that appealed to the general literate public.
Patrons, both ladies and gentleman, paid subscriptions to have access to libraries both large and small and could borrow an unlimited number of books of every topic, many in other languages such as French and Italian, as well as periodicals. Subscriptions ranged from annual to monthly. Typically, a person could borrow up to two books at a time and had a limited number of days in which to read. One source suggested that for an additional fee, a person could borrow multiple books. Since many novels came in at least three parts, such a temptation would be hard to resist since I'm sure many readers share my dislike of waiting for the next part in a story to become available.
Besides being a place to borrow books, or simply sit and read in the reading room, circulating libraries became a fashionable place to see and be seen. They sprang up in resorts towns like Brighton where the locals and visitors mingled and relaxed.
In addition to offering a selection of books printed by publishers, circulating libraries also became their own publishers and were friendly to female authors. Minerva Press, so well known for printing Gothic novels, was one such publisher who gave voice to a number of women who penned novels. Such publishers changed to course of publishing and really opened the door to the social acceptability of female authors, as well as created a better variety of fictional novels.
As books became less expensive to print, partly due to the paperback cover and using cheaper materials making it more affordable to readers, and as public libraries were created which offered books for free, the circulating library fell out of popularity. But their influence shaped the future for readers, authors and publishers. And I, for one, am eternally grateful for them paving the way for me to realize my dream of becoming a published author.