Whilst general relativity is not complex in its formulation, the physical interpretation of its mathematical descriptions gives rise to a range of exciting consequences in cosmology. A detailed understanding of general relativity is therefore a prerequisite for students wishing to pursue further courses or commence research projects in cosmology and its various captivating subfields including black holes and gravitational waves. This is not a book on general relativity per se and the author’s treatment of this fundamental topic is concise, with the required differential geometry summarized in an appendix. Instead, the primary goal of this book is to allow students to understand in a critical way two pillars of modern theoretical physics: inflationary theory, and quantum black holes and the information—loss problem. Accordingly, the book extensively introduces black holes and cosmology before proceeding to the important issues found in inflation and the information—loss problem. Other important topics discussed in detail include the cosmological constant and its relation to dark energy and an introduction to quantum field theory on curved backgrounds. Including numerous exercise problems, the material provides a single rigorous text for advanced students in theoretical physics and mathematics requiring an introduction to the implications and interpretation of general relativity in areas of cosmology. Readers of this text will be well prepared to follow the theoretical developments in the field and undertake research projects as part of an MSc or PhD programme.