St. Catherine is one of the three Dominican doctors of the church (we'll get to the others later), and one of only four women Doctors of the Church (along with St. Therese of Lisiuex, St. Teresa of Avila, and St. Hildegard of Bingen). 

She was the 24th (YES, twenty-fourth!) child (out of an eventual 25) born to her parents, Lapa and Giacomo di Benicasa. Giacomo was a cloth dyer. Catherine was born n Marc 25, 1347 in Siena, Italy, and was one of a pair of twins. Her sister, Giovanna, died soon after their birth. As a child, Catherine (or in Italian, Caterina) was so happy that her nickname was "Euphrosyne", which means joy in Greek. 

Catherine had her first vision when she was five or six. On her way home with her brother, she saw Christ in glory, attended by the apostles Peter, John, and Paul. At age 7, she vowed her entire life to God. This vow was tested at the age of 16, when her sister died, and her parents tried to force her to marry her sister's husband. Catherine undertook a severe fasting regime as part of her prayer against being married against her will, and her prayers were answered. From these experiences, she later said that people should "build a cell inside your mind, from which you can never flee." Catherine maintained a constant state of prayer and awareness of God, even when she was outwardly attending to other things. 

Catherine chose to live an active and prayerful life, not becoming a mother or a wife, but also not becoming a nun. After a period of severe illness, Catherine's mother took her to the local "Mantellate", or third order Dominicans, and asked them to take her daughter. Catherine received the Dominican habit from the local friars, despite the strenuous objections of the Mantellate, for up until that time the women had all been widows. Catherine lived at home in almost total silence and solitude. She often gave away her family's food and clothing to the poor.

At about age twenty-one, Catherine experienced a "mystical marriage" with Jesus, where she received a ring that only she could see. After this, she gradually retreated from her life of solitude and entered the work and life of her family, and began helping the ill and poor of Siena, working in hospitals and in the homes of the sick. Other people were drawn to Catherine's joy and piety, and began to help her in her works. 

If this was all St. Catherine did, she would still be a commendable example of the Dominican charism and saintly behavior. But she did even more. Only taught to read by the Mantellate, Catherine could not write, but yet she felt drawn into the wider world of politics. She traveled through northern and central Italy advocating reform of the clergy and advising people on the spiritual life. She fought to have the papacy returned to Rome from Avignon, and kept up correspondence with Pope Gregory XI, through which she asked him to reform the clergy and the administration of the Papal States. She eventually convinced him to return to Rome and take up residence there. Her involvement with the papacy is why she is often seen holding a boat in art--the boat is the Barque of St. Peter. 

In 1377, she learned to write, and wrote her Dialogue of Divine Providence, still relying on her secretaries for writing some of her correspondence. The Dialogue is her major work, and was written between October of 1377 and November of 1378. It is a dialogue between the soul and God Himself, and much of it was written while Catherine was in deep ecstasy. Her letters are considered great works of Tuscan literature, and some 300 of them survive. 

She died in Rome on April 29, 1380 at the age of thirty-three. 

Throughout her life, she practiced rigorous abstinence from food. She was a daily communicant and also received the stigmata. Catherine's mother, Lupa, helped Catherine's confessor, Bl. Raymond of Capua, O.P., write her daughter's biography. She was canonized in 1491 and named a Doctor of the Church by Pope Paul VI in 1970. 

Her feast day is April 29th, and she's the patron of illness, Italy, Europe, miscarriage, the sick, nurses, sickness, and the saint to invoke against fire. 

Possibly her most famous quote is: If you are what you should be, you will set the world on fire (from her letters).