The exact origins of Lincoln’s Inn, and indeed of the other three Inns of Court, are not fully known. The extant records of Lincoln’s Inn open in 1422, the earliest of any of the Inns of Court; but a society of lawyers by that name was then already in existence. It is likely that it evolved during the late part of the fourteenth century. In contrast to many of the colleges of Oxford or Cambridge, which it resembles, there was no conscious founding or dated charter.
First, why “Inn”? As well as applying to the houses used by travellers and pilgrims - the usage that usually comes to mind - the term, or its Latin equivalent hospitium, also applied to the large houses of magnates of all kinds, such as statesmen, bishops, civil servants, and lawyers, whose business brought them to town, especially when Parliament and the courts were in session. The area in which many were situated were then suburbs, salubrious but convenient for both Westminster and the City. This type of inn was often not simply an individual residence but provided accommodation for a whole retinue of guests and typically included, both as a focus for medieval living arrangements and as a status symbol, a hall (indeed, the bishops’ inns were also called palaces). Law students, or “apprentices” of law, who at the period learnt their craft largely by attending court, sought shared accommodation during the legal terms, sometimes in part of an inn of a magnate who did not need it.
Originally there were at least twenty inns associated with lawyers. Gradually these became places of legal education and there emerged the four principal Inns of Court (ie Inns of the men of Court) that we know today. The other Inns became known as the Inns of Chancery. You may come across their names, such as Staple Inn or Clement’s Inn, in the vicinity. They were treated at first as preparatory schools for the main Inns of Court and then during the seventeenth century became the Inns exclusively for attorneys (ie solicitors) and clerks (they had all vanished as societies by the beginning of the twentieth century).
The term “barrister” was originally a purely internal or domestic rank - a graduate of the Inn who had successfully negotiated the elaborate legal exercises set in Hall, which was laid out for moots like a court, with a bar. Although there were various attempts to regulate those who appeared in court, any requirement that they be barristers of an Inn of Court emerged at first only as a matter of practice - a case in 1590 finally confirmed it as a matter of law. And once that happened the process of excluding mere attorneys from membership of the Inns of Court was accelerated.
The recognition of barristers’ exclusive right of audience was no doubt due in part to the thoroughness of the original medieval system of legal education provided by the Inns - at least seven years between admission as a student and call to the bar. That system completely broke down with the English Civil War in 1642. It has to be said that legal education in the Inns from then until the nineteenth century, or later, cannot be regarded as the most glorious part of their history. The old residence requirements for students were diluted into the mere ritual of dining and the old exercises were reduced to the perfunctory formality of reciting the first few lines of a standard formula from a pre-prepared card. Bar exams were only introduced in 1852 and were not even compulsory until 1872, and in any event could be passed by anyone with a modicum of application with a few weeks study. So, a far cry from today.
Then, why “Lincoln’s” Inn? Tradition has it that the name comes from Henry de Lacy, third Earl of Lincoln (d. 1311) whose own house was nearby and may have been patron of the Inn. Tradition is not to be entirely gainsaid and indeed the Earl’s arms form part of the Inn’s arms, but it is more likely that the name came from Thomas de Lincoln, one of the serjeants at law (senior practitioners, before the days of QCs) during the fourteenth century.
You can read more on all aspects of the Inn, past and present, in the beautifully produced book, A Portrait of Lincoln's Inn - sadly,now out of print, though a copy can be viewed in the Library (members only). A small colour brochure, An Introduction to Lincoln’s Inn, originally written by the late Sir Robert Megarry, is available from the Treasury Office.