Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Abhas Mitra is a noted Indian astrophysicist and is known for his trait of novel thinking on several frontline astrophysics problems. He is the first astrophysicist to suggest that photo-meson process rather than proton-proton collision process could be the leading mechanism for Ultra High Energy gamma-ray production in ultra-compact X-ray binaries. As far as India based astrophysicists are concerned, he was the first to carry out research on various theoretical aspects of modern Gamma Ray Burst paradigm.