Although the connective tissue attachment represents the key issue in periodontal health or disease and in periodontal therapy, the assessment of alveolar bone changes renders valuable indirect evidence for periodontal stability, progression of disease, or repair mechanisms. In periodontal disease bacterial products trigger host cells to release mediators, which may imbalance the steady state between resorption of bone and apposition of osteoid. Modulation of the hosts prostaglandin or interleukin-I synthesis by drug therapy could support the antimicrobial concept of periodontal therapy. Cross-sectional and long-term assessments of alveolar bone have been used to estimate the progression rate of periodontal disease. Inherent limitations of bone assessments in radiographs have to be considered when drawing conclusions from measurements that represent remodeling in periodontal lesions after therapy. Both bone quantity and quality seem to be of secondary importance with respect to the progression of disease, as well as response to therapy. Other risk factors that affect the microbial ecology and/or the hosts immune system seem to be the primary determinants for the periodontal health status.