Letters by a Modern Mystic is a collection of excerpts from the letters of missionary Frank C. Laubach. Written between January 1930 and January 1932, these intimate writings show a faithful man's work to become closer to God through daily, hourly, and minute-by-minute practice.

Frank C. Laubach (1884-1970) was an American missionary and literacy advocate. After graduating from Princeton University (1909), Union Theological Seminary (1913), and Columbia University (Ph.D., 1915), he and his wife Emma sailed to the Philippines to begin their missionary life. They worked among the local Catholic population and spent seven years building evangelical churches on Mindanao, one of the largest Philippine islands. Laubach was later appointed to the faculty of Union Theological Seminary, helping to establish the campus in Manila. During this time, he wrote the book The People of the Philippines, a history of the islands and of religious life there.

After 14 years in the Philippines, Laubach traveled to Dansalan (renamed Malawi in 1956) to work with the Muslim Moros people. Finding them resistant to his evangelical message, he thought that a focus on literacy would be a better method for reaching them. He felt that approaching the Moros people with education and "a divine love which will speak Christ to them though I never use his name" would lead to greater results. His "each one teach one" method of learning to read spread quickly, leading to an explosion of literacy on the island.

During his time at Dansalan, Laubach was alone, his wife and son remaining on another island for health and education purposes. Laubach combatted his loneliness by writing letters to his father about his work, his faith, and his "deep mystic experience of God."