Gertrude the Great or Gertrude of Helfta (January 6, 1256 – November 17, 1302) was a German Benedictine nun and mystic who was a member of the Monastery of Helfta. While herself a Benedictine, she had strong ties to the Cistercian Order; her monastery in Helfta is currently run by nuns of the Cistercian Order.

Little is known of the early life of Gertrude, who was born on the Feast of the Epiphany, January 6, 1256, allegedly in Thuringia (within the Holy Roman Empire). At age five, she entered the monastery school at St. Mary at Helfta (variously described both as Benedictine and as Cistercian), under the direction of its abbess, Gertrude of Hackeborn. It is speculated that her devout parents offered her as a child oblate to the church. However, given that Gertrude implies in the Herald that her parents were long dead at the time of writing, it is possible that she entered the monastery school as an orphan.

Gertrude was entrusted to the care of Mechtilde, younger sister of the Abbess Gertrude, and joined the monastic community in 1266. It is clear from her writings that she received a thorough education in a range of subjects. She, and the nun who authored Books 1 and 3-5 of the Herald, are thoroughly familiar with scripture, the Church Fathers such as Augustine of Hippo and Gregory the Great, and also contemporary spiritual writers such as Richard and Hugh of St. Victor, William of St. Thierry, and Bernard of Clairvaux. Gertrude's writing demonstrates that she was well-versed in rhetoric, and her Latin is very fluent.

In 1281, at age 25, she experienced the first of a series of visions which continued for the rest of her days, and which changed the course of her life. Her priorities shifted away from secular knowledge and toward studying scripture and theology. Gertrude devoted herself strongly to personal prayer and meditation and began writing spiritual treatises for the benefit of her fellow nuns. She received "invisible stigmata". Gertrude became one of the great mystics of the 13th century. Together with her friend and teacher Mechtilde, she practiced a spirituality called "nuptial mysticism" in which they came to see themselves as the Brides of Christ.

Gertrude died at Helfta, near Eisleben, around 1302.

Gertrude produced numerous writings, though only some survive today. The longest surviving work is the Legatus Memorialis Abundantiae Divinae Pietatis (known in English today as The Herald of Divine Love or The Herald of God's Loving-Kindness, and sometimes previously known as Life and Revelations), partly written by other nuns. There also remains her collection of Spiritual Exercises. A work known as Preces Gertrudianae (Gertrudian Prayers) is a later compilation, made up partly of extracts from the writings of Gertrude and partly of prayers composed in her style. It is also very possible that Gertrude was the author of a part of the revelations of Mechthild of Hackeborn, the Book of Special Grace.

The Herald is composed of five books. Book 2 forms the core of the work, and was written by Gertrude herself; she states that she began the work on Maundy Thursday, 1289. Books 3, 4, and 5 were written by another nun, or possibly by more than one, during Gertrude's lifetime and probably at least in part at her dictation. Book 1 was written shortly before or after Gertrude's death as an introduction to the whole collection; it is possible it was written by Gertrude's confessor, but more probably by another Helfta nun.

Gertrude was notable for her veneration of the Sacred Heart of Jesus. Her Herald of Divine Love vividly describes her visions of Christ's heart. Such devotions were based on the belief that Christ's heart poured forth a redemptive fountain through the wound in his side, an image culminating in a famous articulation by Bernard of Clairvaux in his commentary on the Song of Songs. The women of Helfta—Gertrude foremost, who surely knew Bernard's commentary, and to a somewhat lesser extent the two Mechthilds, Mechthild of Magdeburg and Mechthild of Hackeborn—made this devotion central to their mystical visions. Gertrude reported a vision on the Feast of John the Evangelist. She was resting her head near the wound in the Christ's side and hearing the beating of his heart. She asked John if on the night of the Last Supper he had felt these pulsations, why he had never spoken of the fact. John replied that this revelation had been reserved for subsequent ages when the world, having grown cold, would have need of it to rekindle its love.