The most powerful way of making progress in particle physics is to build a new collider with a larger energy. The best option for this is a project called the International Linear Collider, which is a linear e+e- collider with energies in the range of (250-1000) GeV. It will be a complex, mega-scale project, requiring the cooperation of thousands of scientists and engineers from all over the world. This book discusses its importance and the possible new discoveries that can be expected with this collider.