This second edition of Particles in the Dark Universe has been substantially enhanced with several new chapters that delve into crucial aspects of particle physics in the Universe. These additions encompass the role of primordial black holes in the early universe, tracing their formation to decay, unification theories, a comprehensive historical overview of cosmological models, an extensive examination of the physics of the graviton, and an educational exploration of gravitational phenomena such as Unruh-type or Hawking radiation. Additionally, this edition incorporates 30 new exercises and provides a comprehensive presentation of inflationary models, along with a pedagogical insight into the mechanism of baryogenesis. Structured in a logical sequence, this book offers a thorough and instructional exploration of particle physics within the early universe. It initiates by elucidating the thermal history of the universe, delving into pivotal concepts like Big Bang nucleosynthesis, the cosmic microwave background (CMB), and inflation. Subsequently, it meticulously addresses both direct and indirect detection methods of dark matter, followed by an in-depth analysis of neutrino physics. The book further scrutinizes potential candidates for dark matter and their interactions. Designed for theoretical physicists engaged in particle physics within the universe, dark matter detection, astrophysical constraints, and those interested in models of inflation or reheating, this book also caters to astrophysicists involved in quantum field theory computations. It encompasses all essential elements required for computing various physical processes, providing mathematical tables, necessary thermodynamic functions for the early universe, and Feynman rules. Consequently, this book serves as an intersecting point between astrophysics, particle physics, and cosmology.