In the late Middle Ages it became common practice for those who could afford it to create religious foundations called chantries. These foundations could take a wide variety of institutional forms, from altars or small chapels served by individual priests to great colleges such as St George's itself with a huge community. But common to all chantries was the basic requirement that prayers, Masses and the Office should be offered for the good of the founders during their lives and for their souls after death. Many were also intended to serve a charitable or educational role, as in the case of the medieval colleges of Oxford and Cambridge or some of the numerous surviving almshouses of the period. Others provided extra priests and singers to assist in the Divine Service of parish churches.

St George's Windsor is among the most important and ambitious medieval chantry foundations to have survived in England. Indeed the college founded by Edward III was to be of defining importance - both architecturally and institutionally - to the subsequent history of these institutions. But, confusingly, over the course of its medieval history the college also came to serve as an umbrella institution for lots of independent chantries.

Several prominent courtiers, deans and canons chose to establish chapels or altars within St George's, which they built and staffed at their own expense. Evidence for these small foundations is everywhere apparent in the form of screens, spaces for lost altars and, most remarkable of all, several medieval inscriptions exhorting passers by to pray for the souls of certain deceased individuals.

Edward IV actually made his chantry and funeral monument an integral feature of the new chapel in 1475, though this was never finished. Henry VIII also intended a chantry to be set up here as well as a gigantic monument in the centre of the choir. This is despite the fact that he instituted the religious changes which brought about the Reformation in England and the eventual suppression of chantries. All that survives at Windsor of his projected monument are copies of the great bronze candlesticks intended to surround the tomb. Attempts were made to complete Henry's monument (which lay unfinished) by both his daughters, Mary I and Elizabeth I. Neither succeeded fully in their plans but Elizabeth did manage to reconstitute the Poor Knights attached to the college as a community of thirteen men in accordance with her father's wishes.

The status of the college as a royal foundation saved it from dissolution at the Reformation, and this circumstance served in turn to preserve many of the smaller chantries within it. These remain, in fact, the only chantries of their kind in England which have never formally been suppressed.