This book is for folks that build acoustic guitars and similar instruments like ukuleles and acoustic bass guitars that want to begin doing design work but do not necessarily have technical backgrounds. The term "design work" describes both structural modifications to the instrument and esthetic changes to the instrument body. Structural modifications range from very simple things like designing string sets to support alternate tunings, to more complex efforts like designing completely new instruments for nontraditional pitch ranges. Although all such engineering can be done by trial and error, this book discusses more reliable and less time-consuming approaches that help the designer get it right the first time. The material is presented in design order, starting with the pitch range of the instrument to be designed, proceeding to the design of the scale length and string set for that pitch range, and continuing with the size, shape, and structure of the instrument body. Also provided is basic design information in a math-free format that is easy to understand. The design approaches discussed here make use of free online instrument design software, including the "G" Thang Acoustic Guitar Design Tool. The book also serves as the user's manual for "G" Thang. This software enables the designer to use powerful design technology without complicated engineering math.