This book provides a broad introduction to the physics and technology of the High Luminosity Large Hadron Collider (HL-LHC). This new configuration of the LHC is one of the major accelerator projects for the next 15 years and will give new life to the LHC after its first 15-year operation. Not only will it allow more precise measurements of the Higgs boson and of any new particles that might be discovered in the next LHC run, but also extend the mass limit reach for detecting new particles. The HL-LHC is based on the innovative accelerator magnet technologies capable of generating 1113 Tesla fields, with effectiveness enhanced by use of the new Achromatic Telescopic Squeezing scheme, and other state-of-the-art accelerator technologies, such as superconducting compact RF crab cavities, advanced collimation concepts, and novel power technology based on high temperature superconducting links. The book consists of a series of chapters touching on all issues of technology and design, and each chapter can be read independently. The first few chapters give a summary of the whole project, of the physics motivation and of the accelerator challenges. The subsequent chapters cover the novel technologies, the new configurations of LHC and of its injectors as well as the expected operational implications. Altogether, the book brings the reader to the heart of technologies for the leading edge accelerator and gives insights into next generation hadron colliders.