In this book, extensive information regarding the field of cosmology has been provided. During the past few years, it has been witnessed that the field of cosmology has experienced a metamorphosis. From primarily being a search for three essential numbers - the cosmological constant, the expansion rate and deceleration parameter, it has now transformed into a precision science. This scientific domain is expected to unveil even the minutest details of fundamental processes that took place during initial stages of the Universe and also of the mechanisms driving the cosmic expansion and the progress of structures at the largest scales. For the achievement of these aims, we not only need formulation of novel observational and experimental strategies but also an in-depth comprehension of the underlying theoretical frameworks. Veteran researchers and scientists from across the globe have contributed significant information in this book.