This book deals with - inflationary model building and estimation of cosmological parameters from various quantum field theoretic setup, quantification of reheating temperature, studies of leptogenesis in braneworld and estimation of primordial non-Gaussianity from ${\cal N}=1$ supergravity using $\delta N$ formalism. The main motivation of this book is to give a complete overview of early universe inflationary cosmology model building based on the prescription of quantum field theory in curved space-time (de Sitter space) to the general readers.