Mother Teresa to become St Teresa of Calcutta later today
Mother Teresa, the Nobel peace laureate who died 19 years ago, will be known as St Teresa of Calcutta following her canonisation by Pope Francis today.
More than 100,000 pilgrims are expected to attend the service in St Peter's Square at the Vatican, to honour the nun who worked in the slums of the Indian city now known as Kolkata.
Thousands attended a papal audience on Saturday in the Vatican, where a large canvas of the late nun in her blue-hemmed white robes hung from St Peter's basilica.
The Church defines as saints those believed to have led such holy lives they are now in Heaven and can intercede with God to perform miracles - two of which are needed to confer sainthood.
She is credited with healing an Indian woman from stomach cancer in 1998 and a Brazilian man from a brain infection in 2008.
Many pilgrims arrived at the Vatican before dawn on Sunday to get a good spot for the Mass.
Some 1,500 homeless people across Italy are also being brought to Rome in buses to be given seats of honour at the celebration - and then a pizza lunch served by 250 nuns and priests of the Sisters of Charity order.
Large TV screens were set up at Mother House in Kolkata (Calcutta) for the Vatican ceremony.
Senior sister at the Mother House, Mary Lysa, said: "It's a day of rejoicing, a day of gratitude and a day of many, many blessings."
Mother Teresa founded a sisterhood that runs 19 homes, and won the Nobel Peace Prize.
But she was not without her critics, as some people noted a lack of hygiene in the hospitals run by her sisterhood, and said she accepted money from dictators for her charity work.