The idea of inflationInflation had been developed to solve the “horizon problemHorizon problem” of why there were larger correlations than the horizon size in the early universe and the “flatness problemFlatness problem” of why curvature of the universe remains almost zero even after more than 10 billion years [Gut81, Sat81, Sta80, Lin82, AS82]. Taking those thoughts for granted, this book focuses on another important role of inflation: the generation of primordial fluctuations, which give the initial conditions of the current universe.