Two primary historical sources are available to scholars of medieval English law: the official court records or plea rolls, and the unofficial court reports, most notably the year books, which apparently were the work of professional court reporters.
Plea rolls, as the official records of the court, were written in Latin. There were usually two copies of each roll, one inscribed with the name of the Chief Justice, and known as the Chief Justice's Roll and the other with "Rex" and known as the King's Roll. The Rolls provide a concise and exact account of the proceedings in the various cases that came before the Court, including the names of the parties to an action, the nature of the action, the plaintiff's statement of his case, the defendant's defense, and the pleas upon which both parties finally rested their case, the verdict of that jury, if one were ever delivered, and the judgment of the Court upon that verdict. The object of the record was to provide a clear and final statement, which bound all parties.
The year books record the arguments of the serjeants who were authorized to plead before the justices of the King's Court of Common Bench at Westminster Hall, the reports of trials when the justices went on their periodic eyres to the counties, and the reports of trials before the country justices in the assizes held in the larger market towns. Written in Law French, they were intended for the use and instruction of the legal profession, and record all the procedural moves made in an action, since apparently they were intended to guide serjeants in determining what would be the best line of argument to take up, and what form of plea he should make in subsequent actions. According to William Bolland, they were most likely the work of professional reporters probably juniors or apprentices, perhaps sponsored by a syndicate of Serjeants, who sold their works to members of the legal profession (Bolland, William C. A Manual of Yearbook Studies. Cambridge, Cambridge University Press, 1925 at p.37). The earliest extant examples date from 1268 and they continued to be compiled until 1535.
Maxwell and Brown's compilation on British law reports (Maxwell, William H. and Charles R. Brown, A Complete List of British and Colonial Law Reports and Legal Periodicals. Toronto, Carswell, 1937.) gives a chronological listing of court reports under each of the separate courts, Curia Regis, King's Bench, Court of Common Pleas, Chancery etc., and for a more detailed classification of court records in the Public Record Office, see the first volume of the Guide to the Contents of the Public Record Office (Great Britain. Public Record Office. Guide to the Contents of the Public Record Office. London, HMSO, 1963-1968). For the purposes of this guide, the records are grouped by broader categories, such that all court records, for example of the Curia Regis, King's Bench, and Court of Common Pleas are listed under the general heading, "Central Common Law Courts."
It is important to note that, in spite of all the published sources already listed here, there still remain medieval case law reports in unpublished manuscript form for future scholars to discover. Also there are almost certainly digitization projects planned or underway which will make this material available to medievalists worldwide.