Thérèse de Lisieux (French: Thérèse de Lisieux; born Marie Françoise-Thérèse Martin; 2 January 1873 – 30 September 1897) was a French Discalced Carmelite nun who is widely venerated in modern times. She is popularly known in English as the Little Flower of Jesus, or simply the Little Flower, and in French as la petite Thérèse ("little Therese").

Thérèse has been a highly influential model of sanctity for Catholics and for others because of the simplicity and practicality of her approach to the spiritual life. She is one of the most popular saints in the history of the church, although she was obscure during her lifetime. Pope Pius X called her "the greatest saint of modern times".

Thérèse felt an early call to religious life and, after overcoming various obstacles, joined the cloistered Carmelite community of Lisieux, Normandy, in 1888 at the young age of 15. She served in various roles during her nine years as a Carmelite nun, including sacristan and assistant to the novice mistress. In her last eighteen months, she experienced a spiritual trial known as a "night of faith" where she felt the absence of Jesus and was tormented by doubts of God's existence. Thérèse died at the age of 24 from tuberculosis.

After her death, Thérèse became known globally through her spiritual memoir, The Story of a Soul, which explains her theology of the "Little Way". Her immense popularity and reputation for holiness led to her quick beatification and canonization by Pope Pius XI, just 28 years after her death. In 1997, Pope John Paul II declared her a Doctor of the Church.

Her feast day in the General Roman Calendar was 3 October from 1927 until it was moved in 1969 to 1 October. The Basilica of Lisieux is the second most popular place of pilgrimage in France after Lourdes.