This book is a record of the complete proceedings of the first International Symposium on Recent Developments in Relativistic Astrophysics (ISRA 2023), convened on December 11 – 13 at Shri Ramasamy Memorial (SRM) University Sikkim, Gangtok, India. The present  volume contains contributions by 50 researchers and distinguished scientists across the globe who are well known scholars in their own right. This volume is a collection of original research reports and reviews on contemporary issues on relativistic astrophysics, astroparticle physics, gravitation, cosmology, and related quantum physics, is a tribute to Prof. Banibrata Mukhopadhyay, a leading Indian astrophysicist of our times, commemorating his 50th birth anniversary, in light of Mukhopadhyay’s illustrious academic journey. This Festschrift  covers a  wide range of topics that includes physics of accretion and relativistic jets, X-ray and gamma-ray astronomy, astrophysical fluids and plasma,  physics of compact objects,  gravitational wave astrophysics,  cosmic ray physics, the dark matter problem and cosmological issues, gravity physics and gravity-quantum interface, astrochemistry and origin of life, and space instrumentation.  A majority of the authors were/are Mukhopadhyay’s PhD students, post-doctoral fellows and his research collaborators. A major part of this document revolves around evolution and diversification of Mukhopadhyay’s own research and his accomplishment, and subsequent evolution of research of his thirty odd doctoral students and post doctoral fellows into diverse fields of astronomy and space science.  The book has been compiled in such a manner so as to present an overview of the contemporary research in relativistic astrophysics and related fields in space science, pointing out future perspectives, and  updating with the latest and most impactful developments  in the field. This volume would prove to be beneficial to potential graduates, doctoral students, young and professional researchers and academicians alike.