The misteries of the Universe have always struck the human mind and challenged its capabilities of knowledge and understanding. How is the Universe evolving? How did stars, galaxies, galaxy clusters, and all the cosmic structures form? When did they form? Were primordial structures similar to the ones which we presently observe? Which are the reasons for their origins? These are among the questions which are addressed in this book: starting from elementary principles and following clear argumentations, the author outlines the properties of our expanding Universe and its cosmological history. The work sketches the current understanding in this field and is therefore well suited not only to professionals, but also to anyone interested more in depth in the investigations on cosmic structure formation.