This chapter reviews the growing body of epidemiological evidence linking long-term exposure to ambient air pollution with increased risk of dementia, including Alzheimer’s disease (AD) and vascular dementia (VaD). With air pollution now recognized as a potentially modifiable risk factor, the chapter explores mechanistic pathways, such as neuroinflammation and oxidative stress, through which pollutants like PM2.5 and NO₂ may contribute to neurodegeneration. It discusses dementia subtypes, highlighting the need for subtype-specific analyses given their differing pathologies and risk factors. The chapter also emphasizes the importance of life course exposure assessment and the potential roles of co-exposures such as noise and lack of green space, which are often correlated with air pollution but understudied in relation to cognitive decline. A review of systematic reviews and meta-analyses reveals consistent associations between PM2.5 and dementia risk, though evidence remains limited for other pollutants. The chapter calls for future studies to adopt multi-exposure frameworks, improve exposure and outcome assessments, and include underrepresented populations in high-pollution areas, particularly in low- and middle-income countries. Establishing a causal link between air pollution and dementia could significantly strengthen the case for environmental interventions as a public health strategy to reduce the burden of dementia worldwide.