TAUP 91 covers the proceedings of the Second International Workshop on Theoretical and Phenomenological Aspects of Underground Physics, held in Toledo, Spain on September 9-13, 1991. The book focuses on the processes, methodologies, reactions, and transformations involved in underground physics. The selection first offers information on the fundamental issues in particle astrophysics and an overview of the problems related to general cosmology. Topics include connections between particle physics, astrophysics, and cosmology, stellar physics and particles, astrophysical ages, cosmic background radiation, and abundances of light elements. The text also takes a look at big bang nucleosynthesis constraints on new physics and microwave background radiation. The publication ponders on very wide band interferometric gravitational wave antenna and search for stellar gravitational collapse by macro. The text also examines high energy cosmic neutrinos of acceleration and non-acceleration origin; tests of general relativity and Newtonian gravity at large distances and the dark matter problem; and nuclear form factors for the scattering of neutralinos. The selection is a valuable reference for readers interested in underground physics.