This self-contained book provides a rigorous, systematic, and up-to-date treatment of the modem theory of factorial design. It includes lots of examples, predominantly from engineering and agriculture, to illustrate the methods. The book incorporates a few exercises in each chapter to enable the book to be used for self-study or for a special topics course. Topics covered include a general theory of multi-stratum factorial design, design key for constructing factorial designs, new construction methods of resolution IV designs, and some results on their structures taken from the literature of projective geometry.