Tsong khapa (14th-15th centuries) is arguably the most important and influential philosopher in Tibetan history. His Ocean of Reasoning is the most extensive and perhaps the deepest extant commentary on N=ag=arjuna's M'lamadhyamakak=arik=a (Fundamental Wisdom of the Middle Way) , and it can be argued that it is impossible to discuss N=ag=arjuna's work in an informed way without consulting it. It discusses alternative readings of the text and prior commentaries and provides a detailed exegesis, constituting a systematic presentation of Madhyamaka Buddhist philosophy. Despite its central importance, however, of Tsong khapa's three most important texts, only Ocean of Reasoning has until now remained untranslated, perhaps because it is both philosophically and linguistically challenging, demanding a rare combination of abilities on the part of a translator. Jay L. Garfield and Geshe Ngawang Samten bring the requisite skills to this difficult task, combining between them expertise in Western and Indian philosophy, and fluency in Tibetan, Sanskrit, and English. The resulting translation of this important text is not only a landmark contribution to the scholarship of Indian and Tibetan Buddhism, but will be invaluable to students of Tibetan Buddhism and philosophy, who will now be able to read this work alongside N=ag=arjuna's masterpiece.