This book presents a study of inflationary dynamics of the early Universe in the large extra-dimensional braneworld cosmology. We first provide an introduction to the standard cosmology. Motivated by some of its shortcomings, we introduce the theory of cosmic inflation followed by the detailed derivations of scalar and tensor power spectra. We also discuss the mechanism for reducing the tensor to scalar ratio in Gauss-Bonnet inflationary models. In braneworld, Friedmann equations are modified to include a quadratic term in energy density.We review some of the essential ingredients of swampland program, and discuss its constraints on the theory of cosmic inflation.In particular, the tensor-to-scalar ratio can be reduced without changing the spectral index. Moreover, the constraints on the slope of the potential can be relaxed that are important to realize de Sitter Universe supported by observations.