Ahmad Sirhindi (d. 1624 in northern India), the most important sufi of the 16^th century, is the founder-figure of the renowned Naqshbandi-Mujaddidi sufi lineage. His principal teachings are contained in his 1263-page Collected Letters, which are written mostly in Persian. There are few other sufi texts on a pan-Islamic level that have had and continue to have such a lasting impact on Muslims in the eastern Islamic world. Buehler’s translation is the first time that entire letters of Sirhindi’s Collected Letters have been translated into English. Now the English-speaking world has access to the spiritual experiences and contemplative practices of a great sufi, whose spiritual descendants make the Naqshbandiyya-Mujaddidiyya one of the most influential sufi lineages in the contemporary world.