The official process for declaring someone a saint is called Canonisation. Prior to the year 1234, the Church did not have a formal process as such. Usually martyrs and those persons recognised as holy were declared saints by the Church at the time of their deaths. Before the legalisation of Christianity in the year 313 by Emperor Constantine, the tombs of martyrs, like St. Peter, were marked and kept as places for homage. The anniversaries of their deaths were remembered and placed on the local Church calendar. After legalisation, oftentimes basilicas or shrines were built over these tombs.
Pope Gregory IX Approving the Decretals
As time went on, the Church saw the need to tighten the Canonisation process. Unfortunately, sometimes figures of legends were honoured as saints. Therefore, in the year 1234, Pope Gregory IX established procedures to investigate the life of a candidate saint and any attributed miracles. In 1588, Pope Sixtus V entrusted the Congregation of Rites (later named the Congregation for the Causes of the Saints) to oversee the entire process. Beginning with Pope Urban VIII in 1634, various Popes have revised and improved the norms and procedures for Canonisation.
Fr William Woestman O.M.I. in his book, ‘Canonization – Theology, History, Process’ gives a very detailed explanatory of the current process leading up to Beatification and Canonisation. This work interprets in layman terms the formal SANCTORUM MATER from the Vatican’s Congregation for the Causes of Saints (i.e. INSTRUCTIONS FOR CONDUCTING DIOCESAN OR EPARCHIAL INQUIRIES IN THE CAUSES OF SAINTS). A Cause for Canonisation cannot be started unless there exists a true and widespread reputation among the faithful that a deceased person is in heaven because either the Servant of God gave the supreme witness of faith by sacrificing his or her life (i.e. a martyr) or because the person lived in a continuous heroic manner in all the Christian virtues of Prudence, Justice, Fortitude, Temperance, Faith, Hope and Charity.