This article provides a critical review of biomechanical modeling approaches used to estimate spinal loads, stability, and risk of injury. The complete biomechanical analysis of the spine requires a two-stage approach: (1) equilibrium analysis for estimating tissue loads, and (2) stability analysis for estimating structural tolerance of the spine. For each level of analysis, basic principles are reviewed and relevant published models and studies are referenced. Throughout the article, implications for lumbar function and dysfunction derived from the various modeling methods are presented, and their applications are discussed. At the end, future directions for research are identified. Detailed descriptions of selected modeling approaches are provided in the appendices.