This book complements the popular series on theoretical physics by Professor Fliessbach. Readers will find in this book the fundamentals of general relativity, starting with special relativity and the physical and mathematical foundations of GR. It then discusses static gravitational fields, gravitational waves, and star models. The final chapters are dedicated to cosmology. This book is appreciated and recommended by students and lecturers who engage with theoretical physics in a course lecture for its clear and well-structured presentation of the material. The author provides a clear physical discussion of matter and also explains the challenging mathematics in an understandable way. The book includes more than 40 exercises with solutions. In the seventh edition, this book has been updated.