For the first time since 1676, an annotated reissue of the Letters for the exercise of mental prayer by Miguel de Molinos is published. Its author, the most important figure of Spanish Quietism, indicates the steps to inner emptiness through the suspension of desire as a means to achieve peace and hence contemplation: the mystical union. Halfway between Christianity and Buddhism, in the midst of the European Baroque, these Letters represent a more pedagogical development of his Spiritual Guide, which had to wait until 1935 to see it reissued, and of his Defense of Contemplation, which was not reissued until 1983.