The Tantrasa?graha, composed by the renowned Kerala astronomer N?lakantha Somay?j? (c. 1444?1545 AD), ranks along with the ?ryabha??ya of ?ryabha?a and the Siddh?nta?iroma?i of Bh?skar?c?rya as one of the major works which significantly influenced further work on astronomy in India. One of the distinguishing features of this book is the introduction of a major revision of the traditional Indian planetary model. N?laka??ha arrived at a unified theory of planetary latitudes and a better formulation of the equation of centre for the interior planets (Mercury and Venus) than was previously available. In preparing the translation and explanatory notes, the authors have used authentic Sanskrit editions of the Tantrasa?graha by Surand Kunjan Pillai and K. V. Sarma. All verses have been translated into English, which have been supplemented with detailed explanations including all necessary mathematical relations, illustrative examples, figures and tables by using modern mathematical notation. The book includes a glossary of frequently occurring Sanskrit terms and several appendices that serve to clarify many concepts relevant to the topics discussed in the main text.