What is canonisation and how did Mother Teresa become a saint?

For many of the poor and destitute whom Mother Teresa served, the tiny nun was a living saint. Many at the Vatican would agree, but the Catholic Church nevertheless has a grueling process to make it official, involving volumes of historical research, the hunt for miracles and teams of experts to weigh the evidence.

In Mother Teresa's case, the process will come to a formal end tomorrow when Pope Francis declares the church's newest saint.

Here's a look at the process:

The process to find a new saint usually begins in the diocese where he or she lived or died; in Mother Teresa's case, Kolkata.

A postulator - essentially the cheerleader spearheading the project - gathers testimony and documentation and presents the case to the Vatican's Congregation for the Causes of Saints. If the congregation's experts agree the candidate lived a virtuous life, the case is forwarded to the pope, who signs a decree attesting to the candidate's "heroic virtues." If the postulator finds someone was healed after praying for the candidate's intercession, and if the cure cannot be medically explained, the case is presented to the congregation as the possible miracle needed for beatification, the first major hurdle in the saint-making process.

Panels of doctors, theologians, bishops and cardinals must certify that the cure was instantaneous, complete and lasting - and was due to the intercession of the saintly candidate. If convinced, the congregation sends the case to the pope, who signs a decree saying the candidate can be beatified. A second miracle is needed for the person to be declared a saint.

The saint-making process has long been criticized as being expensive, secretive, ripe for abuses and subject to political, financial or theological winds that can push one candidate to sainthood in record time and leave another languishing for centuries.

Pope Francis has raised eyebrows with some rule-breaking beatifications and canonizations, waiving the need for miracles and canonizing more people in a single clip - more than 800 15th-century martyrs - than John Paul did in his 26-year pontificate (482).

Francis has also imposed new financial accountability standards on the multimillion-dollar machine after uncovering gross abuses that were subsequently revealed in two books. The books estimated the average cost for each beatification at around €500,000 ( $550,000), with much of the proceeds going to a few lucky people with contracts to do the time-consuming investigations into the candidates' lives.

For the record, the postulator of Mother Teresa's cause says her case, which stretched over 20 years, cost less than 100,000 euros.