An eyre was, in its most fully developed form, a comprehensive judicial session for a single county, dealing with criminal, civil and other pleas, usually held by a group of justices who visited a number of counties in turn. Eyres began some time before 1194, probably in the 1170s, and were held regularly until 1294, after which their use was only occasional and in individual counties. The last summons for an eyre was issued in 1374, but it was not held, and the last eyre to produce any records was that in Kent in 1348. Eyre functions thereafter either lapsed or were taken over by justices of assize or of oyer and terminer. Separate eyres for forest pleas were also held from the twelfth to the fourteenth century, with revivals under Henry VII and Charles I.
The system of assizes, based on regular journeys by the judges to groups of counties, with fixed stopping places at the more prominent towns, which was to continue down to the Courts Act 1971 and the creation of the Crown Court, can be traced to the period of the general eyre. Justices of assize were originally normally commissioned to take only possessory assizes, such as novel disseisin, and not, unlike the justices in eyre, other civil pleas, although they did deal with items of judicial business other than assizes. As early as 1225 there were sessions held by justices commissioned for assizes and gaol delivery jointly. Each assize required an individual commission appointing the justices to hold it. After 1273 the justices worked in fixed circuits, and ceased normally to to deal with non-assize business. After a period of experimentation between 1273 and 1330, the assize justices came regularly to be responsible for gaol delivery also; eventually gaol delivery became the major part of their work. Litigation by possessory assize declined rapidly in the early fifteenth century, but the justices of assize continued to be important in the administration of civil justice because of their nisi prius powers, which date back to the later thirteenth century and which enabled them to take local jury verdicts in cases initiated in the central courts. In going on their circuits the formal business of the assize justices was regulated by the issue to them of five distinct commissions: of the peace; of oyer and terminer; of general gaol delivery; of assize; and of nisi prius.
General oyer and terminer commissions replaced the general eyre in some of its aspects, the justices being appointed to hear and determine a list of offences by whosoever committed in one or more counties. The first comprehensive country-wide commissions of that sort were those of 1305-1307, which were called 'trailbaston', after the vagrants armed with cudgels with whom they were intended to deal. That name continued to be applied to some of the later commissions of the same sort, although, with the exception of occasions like the Peasants' Revolt of 1381, most of the later sessions were mainly concerned to deal with abuses by officials, as many of the the earliest ones had been. From an early date the justices of oyer and terminer heard and determined suits by bill between parties, as the general eyre had after 1278. The justices reviewed the work of the keepers, later justices, of the peace, not the sheriffs as the eyres had. General sessions of oyer and terminer were fairly frequent during the fourteenth century, and the same powers were also exercised by the court of King's Bench during its travels to hold sessions in provincial towns during the same period. Special commissions of oyer and terminer were issued to deal with specific offences, usually trespasses or groups of them involving the same people, and were issued in Chancery on the chancellor's own authority. They begin earlier than the general commissions, the earliest recorded dating from 1248; a significant number of the earlier commissions were to hear and determine individual appeals of felony. A general commission of oyer and terminer later came to be held by the justices of assize.
Local keepers and then justices of the peace were appointed periodically from the later thirteenth century, and their powers expanded greatly during the fourteenth. They were permitted to hear and determine trespasses and felonies, permanently from 1389 onwards but for some periods earlier in the fourteenth century. Their powers in that respect were general, not limited to specific enquiries, however wide. The labour legislation of 1349 and 1351 was largely enforced by the justices of the peace, except for the years 1352 to 1359. When King's Bench visited a county the justices were bound to hand in to it all their undetermined indictments, and other cases were removed to King's Bench by writs of certiorari or terminari. The surviving rolls therefore date from the period when the court was sometimes peripatetic, which ended in 1421.