This book guides readers (astronomers, physicists, and university students) through central questions of Practical Cosmology, a term used by the late Allan Sandage to denote the modern scientific endeavor to find the cosmological model best describing the universe of galaxies, its geometry, size, age, and matter composition. The authors draw on their personal experience in astrophysics and cosmology to explain key concepts of cosmology, both observational and theoretical, and to highlight several items which give cosmology its special character. These highlighted items are, Ideosyncratic featu.