The interspinous ligaments (ISLs) are short, membrane-covered structures that connect adjacent vertebral spinous processes, contributing to spinal stability. Although often described as thin and membranous, the ISLs exhibit notable anatomical variability in fiber orientation, morphology, and histological structure across cervical, thoracic, and lumbar regions. This chapter synthesizes classical and contemporary findings on the structure, morphometrics, biomechanics, and clinical relevance of the ISLs. While many studies report an anterosuperior to posteroinferior fiber trajectory, recent data suggest region-specific patterns, such as a more horizontal course in the lumbar spine. Histologically, ISLs consist of three distinct regions—anterior, middle, and posterior—with collagen and elastic fibers variably distributed among them. Morphometric studies have quantified their size and tensile strength, highlighting reductions in mechanical integrity with aging. Functionally, the ISLs limit spinal flexion and resist spinous process separation, especially in the terminal range of motion. Clinically, ISL degeneration or injury has been implicated in low back pain, spinal instability, and trauma-related syndromes. Recognition of level-specific anatomical and biomechanical properties may enhance diagnostic precision and inform surgical interventions. This chapter underscores the importance of reevaluating the ISLs as dynamic and clinically significant components of the vertebral column, warranting further anatomical and biomechanical research.