This chapter presents the essential ideas of regular fractional factorial designs. Its sections are as follows: Section 5.1. Initial Fractional Factorial Example Section 5.2. Introduction to Regular Fractional Factorial Designs Section 5.3. Basic Analysis of Regular Fractional Factorial Designs Following this introductory chapter on fractional factorials are six more chapters with additional details and examples. Regarding notation for factors, sometimes we identify factors using subscripts (e.g., x1 for the first factor). In other cases, it is more convenient to avoid the use of subscripts, in which case we will label coded factors using bold uppercase letters or numerals (e.g., A or 1).