This article presents the most common structural foot deformities encountered in clinical practice. The deformities are defined, and the expected compensations at the subtalar joint (STJ) are described. The theoretical consequences of the STJ compensations on proximal and distal tissues are presented. A biomechanical rationale for certain tissue disorders is described. The possible effects of abnormal STJ compensation on osseous development are briefly discussed. Key Words: Foot deformities; Gait; Kinesiology/biomechanics, lower extremity; Lower extremity, ankle and foot; Subtalar joint.