The book is aimed at physics students and professional physicists who wish to understand the basics of cosmology and general relativity as well as the most recent cosmological observations and models. It presents a self-contained introduction to general relativity that is based on the homogeneity and isotropy of the local universe. The simplicity of this space allows general relativity to be introduced in a very simple manner while laying the foundation for the treatment of more complicated problems. The latest cosmological observations and theories are discussed. Emphasis is placed on estimations of the densities of matter and of vacuum energy, and on investigations of the primordial density fluctuations and the nature of dark matter.