Recent years have seen a symbiosis of the fields of elementary particle physics and the astrophysics of the early universe. This text presents the background of the subjects and the latest developments at a level suitable for a physics undergraduate. After introductory chapters on elementary particles and their interactions and role in the expanding universe, the problems and challenges of cosmological asymmetries, dark matter and dark energy are presented, followed by chapters on the growth of cosmic structure, on high energy cosmic rays and on particle processes in stars. A balance is maintained between theory and experiment and the text supplemented with over 100 problems, together with answers and model solutions.