This book summarizes the developments over the past several decades in the field of strong interactions at high energy. This is the first ever book almost entirely devoted to the physics of parton saturation and the color glass condensate (CGC).

Our main goal in this book is to introduce the reader systematically to the ideas, problems, and methods of high energy quantum chromodynamics (QCD). Over the years, these methods and ideas have led to a new physical picture of high energy hadronic and nuclear interactions, representing them as the interactions of a very dense system of tiny constituents (quarks and gluons) having only a small value of the QCD coupling constant. Owing to the high density of gluons and quarks the interactions in such systems are inherently nonperturbative; nevertheless, a theoretical description of these interactions is possible due to the smallness of the QCD coupling. Our main goals in the book are to show how these new ideas arise from perturbative QCD and to enable the reader to enjoy the beauty and simplicity of these emerging methods and equations.

The book's intended audience is advanced graduate students, postdoctoral fellows, and mature researchers from the neighboring subfields of nuclear and particle physics. We assume that graduate student readers are familiar with quantum field theory at the level of a standard graduate-level course based on the textbooks by Peskin and Schroeder (1995) or Sterman (1993).