Flexible flat foot is defined as a disorder which is associated with reduced medial longitudinal arch height and increased hindfoot eversion during weight bearing. In this book, chapter 1 outlines Basic Terminology. Also, Chapter 2 outlines overview of the walking biomechanics in individuals with flat foot compared to healthy ones. This chapter focuses on kinematics, kinetics, and muscle activity during walking in individuals with flat foot compared to healthy ones. Furthermore, Chapter 3 outlines Overview of the effects of foot orthoses on walking biomechanics. Moreover, Chapter 4 outlines the effect of different shoes on biomechanical characteristics of individuals with excessive pronation during different tasks such as walking and running.