Progressive cognitive impairment and its clinical culmination in dementia loom as a major public health problem in the coming generation of older adults, and this fact compels investigation to develop interventions that prevent, delay, or cure. The tools of anatomic pathology have provided key insights into the complex convergence of multiple diseases that commonly contribute to the dementia syndrome and its prodrome in the community setting, and they have suggested some exposures that may modulate disease burden. The tools of clinical pathology, in combination with neuroimaging, have revolutionized the approach to clinical investigation of Alzheimer's disease and are now doing the same with Lewy body disease and vascular brain injury. The tools of anatomic and clinical pathology will continue to contribute to our understanding of these diseases as we advance toward effective interventions for the diseases that commonly cause cognitive impairment and dementia in older adults.