The thoracolumbar spine is the principal load-bearing structure of the body. As such, it is subject to a wide variety of forces that can be described by biomechanical principles. Forces act through vectors, depending on the direction of force and the relative location of the instantaneous axis of rotation. Patterns of failure due to supraphysiologic loading or through the loss of structural integrity may be predicted based on the applied force vectors and the stabilization components lost. An understanding of these forces and their effects on the spine is crucial for the safe and efficacious treatment of spinal deformities.