The SiddhÄntaÅiromaá¹i was composed in 1150 CE by the celebrated mathematician&astronomer BhÄskarÄcÄrya. In the Grahagaá¹itÄdhyÄya part of it, most of the standard calculations and algorithms in Indian astronomy of his times are included. All these are explained in detail with commentary on the text, namely, the VÄsanÄbhÄá¹£ya or MitÄká¹£arÄ . This book is on this part only. All the 460 verses of this part have been translated afresh in this work. Now, it is in the VÄsanÄbhÄá¹£ya that the contents of the verses are expounded in detail. In addition, the detailed derivations and proofs of the statements and algorithms are presented in the upapattis . Study of the vÄsanÄ is indispensable for understanding the methodology of, in particular, and thereby, of Indian astronomers in general. The distinct scientific method of BhÄskara (indeed of the Indian astronomical tradition in general, of which he was a leading exponent), his approach to problems and the ways to solve them, can be understood only when one goes through the commentary and understands it. It is for this reason that the VÄsanÄbhÄá¹£ya has been translated into English for all the verses, for the first time. Explanatory notes based on the vÄsanÄ of BhÄskara have been provided for all the verses in modern notation, with a large number of diagrams to facilitate the understanding. The  first  volume  of  the book comprises  the  three  chapters  on Madhayama (Mean longitudes), Spaṣṭa (True longitudes) and TripraÅna (the  three problems) with   about  300  verses. Scholars working in the  area  of  history  of Indian astronomy and mathematics will  find  the present   work  on  this  major text of   BhÄskarÄcÄrya  with  his  auto-commentary, very valuable . In fact,  anyone with  an undergraduate-level  knowledge  of mathematics and  serious interest in  Indian astronomy will  find  this work very  useful  for  understanding the  subject, as  it  is  reasonably  self-contained.