Spectacular experimental advances in observational cosmology have helped raise cosmology to the status of a genuine science, and it is now possible to test many speculative theoretical issues and to obtain reliable values for the key parameters defining our observable universe. This book has emerged from selected lectures given at the Mexican School on Gravitation and Mathematical Physics by leaders in their field. Conceived as both a broad survey and as topical coverage of the latest developments, it will benefit graduate students and newcomers to this field and provide researchers in the field with a modern source of reference.