The 'Letter to the King' (Suhrllekha) is a 123-stanza epistolary poem that Nagarjuna, considered the 'second Buddha' in the Tibetan tradition, addressed to a monarch of the Satavahana dynasty in southern India during the 2nd-3rd centuries AD. This new translation by José Carte, taken directly from the Tibetan and accompanied by a revealing prologue by Raúl Alonso, presents a fundamental text that bridges early Buddhism and emerging Mahayana. The poem progresses from ethical foundations to the most subtle philosophical reflections. In its verses, Nagarjuna offers the king a spiritual path compatible with his worldly responsibilities: advice on ethical conduct, the practice of mindfulness, impulse control, meditation, and understanding of central concepts such as impermanence, emptiness, and interdependent origination. The work includes more than ninety explanatory notes, a study of the historical figure of Nagarjuna, an analysis of the controversies surrounding his existence and authorship, and a detailed explanation of the dating of the text, whose Tibetan translation dates back to the 9th century during the reign of King Ralpachen. This is an exceptional opportunity to access a classic that reveals the deep friendship between a renouncing philosopher and a monarch, and whose teachings on the 'Four Noble Truths', the 'Eightfold Path' and conditioned origination continue to resonate strongly eighteen centuries later.