Saint Simeon of Solun, a 15th-century saint, was the last bishop of the ancient city of Thessalonica to keep his flock from going into union with Rome, and one of the last Byzantine theologians. He wrote many creations on a variety of theological topics. This small brochure contains two works of St. Simeon on prayer, placed in the fifth volume of the Russian "Kindness": "Interpretation of the prayer Lord, have mercy" and "On the sacred prayer."