The 8th century Indian master Santideva's classic guide to the Buddhist path, the Bodhicaryavatara or 'Entering the Bodhisattva Conduct', is to this day one of the most popular and important works of the Mahayana Buddhist tradition. Presented here in a new English translation, it is supplemented with a detailed commentary composed by Sonam Tsemo (1142-1182), one of the most celebrated masters of the Sakya school in Tibet. The commentary shines a brilliant light on Santideva's great work, clarifying every detail and resolving every difficult point. Translated into English from Tibetan for the first time, the commentary is an invaluable aid for all who wish for a full and deep understanding of the Bodhicaryavatara. Translated by Adrian O'Sullivan, a student of Lama Jampa Thaye for over two decades and a director of Sakya Samten Ling in Santa Monica, California. His previous translations include Tsarchen Losal Gyamtso's 'Opening the Door to Precious Accomplishments' (2005), 'Telescope of Wisdom' (2009) and 'The Lamp that Dispels Darkness' (2013), the latter two being translations of commentaries composed by the great Sakya and Karma Kagyu master Karma Thinley Rinpoche.