This book is a journey toward the minimal supersymmetric standard model
(MSSM) down the orbifold road. After some field theoretic orbifold attempts
in recent years, there has been renewed interest in the physics of string orbifolds and it is time to revisit them. In this book, we take the viewpoint that
the chirality of matter fermions is essential toward revealing the secrets of
Nature. Certainly, orbifolds are an easy way to get the chirality from higher
dimensions.