See W. C. Firebaugh, Inns of the Middle Ages (1924); H. A. Monckton, A History of the English Public House (1969).
Found in Europe, they possibly first sprang up when the Romans built their system of Roman roads two millennia ago. Some inns in Europe are several centuries old. In addition to providing for the needs of travellers, inns traditionally acted as community gathering places.
"Inn" in more recent times has often come to denote a business serving alcoholic beverages, especially in North America, where they are usually alcohol-serving restaurants that have never provided lodging or serviced the needs of travellers.
In Europe, it is the provision of accommodation, if anything, that now differentiates inns from taverns, alehouses and pubs. The latter tend only to supply alcohol (although in the UK the conditions of their licence sometimes require them to have a nominal supply of food and soft drinks). Inns tend to be grander and more long-lived establishments. Famous London examples include the George and the Tabard. There is however no longer a formal distinction between an inn and other kinds of establishment, and many pubs will use the name "inn", either simply because they are long established and maybe were once a Coaching inn, or to summon up a particular kind of image; however, originally an Inn had to provide not only food and lodging, but also stabling and fodder for the traveller's horse(s) and for fresh horses for the Mail coach.
The original functions of an inn are now usually split among separate establishments, such as hotels, lodges, and motels, all of which might provide the traditional functions of an inn but which focus more on lodging customers than on other services; pubs, which are primarily alcohol-serving establishments; and restaurants and taverns, which serve food and drink. (Hotels often contain restaurants and also often serve complimentary breakfast and meals, thus providing all of the functions of traditional inns.) In North America, the lodging aspect of the word "inn" lives on in hotel brand names like Holiday Inn, and in some state laws that refer to lodging operators as innkeepers.
The German words for "inn", "innkeeper", and "innkeeping" illustrate the historical importance of inns. An innkeeper is Wirt (a host), the inn itself is a Wirtshaus (a host's house), and innkeeping is Wirtschaft. The last word literally means hosting or hospitality, but is also used to mean economy and business in general. In the Greek language, the word for economy (oikos "house" + nomos "law") is actually identical to housekeeping.