This book constitutes the contributory talks presented in the Conference on Relativistic Astrophysics and Astroparticle Physics entitled ?Exploring the Cosmos? which was held at University of North Bengal, Siliguri, India during January 27-28, 2011. The book contains several original research works by different authors surrounding some of the most profound questions about the cosmos. Our understanding of the cosmos has improved a lot over the course of the last few decades with many new discoveries and impressive ideas in different fields, particularly in Astronomy, Astrophysics and Astroparticle physics. These have been reflected by the wide-ranging topics discussed in this book which include compact objects and its gravitational phenomena, gamma ray bursts, gravitational lenses, the large-scale structure of the universe, cosmology, solar cosmic rays, secondary cosmic ray flux in the atmosphere, cosmic ray extensive air showers, particle interactions etc.