Abstract
In this chapter, an introductory discussion is provided on the topics of geometric dimension and tolerancing, and its impact on selecting the right manufacturing processes. Also, improvements in measurements provide a need to better understand that variation is unavoidable in manufacturing. However, acceptable levels of variation will result in a good assembly. It is important to understand the limits of this variation. After the development of GD&T, drawings became the main tool for communication among design, manufacturing, testing, etc.