Novel approaches to reduce the risk of cognitive decline and Alzheimer's disease and related dementias (ADRD) in older adults are urgently needed given the aging of the population. Over the past decade, observational research has implicated peripheral hearing loss as being one of the largest potentially modifiable risk factors for dementia that may account for 8-9% of all dementia cases. Hypothesized pathways underlying this observed association may be modifiable with hearing loss treatment consisting of the use of hearing technologies (e.g., hearing aids) and rehabilitative training. The Aging & Cognitive Health Evaluation in Elders (ACHIEVE) study is an ongoing, NIA-sponsored Phase III RCT (R01AG055426, MPIs: Lin/Coresh) investigating whether hearing loss treatment versus an aging education control intervention reduces cognitive decline over a three-year follow- up period. From 2018-19, we recruited 977 adults ages 70-84 with untreated mild-to-moderate hearing loss who were randomized 1:1 at baseline (Year 0) to receive hearing intervention (HI; best-practice hearing services and technologies) versus a successful aging (SA) education control intervention (i.e., one-on-one sessions with a health educator covering topics important for healthy aging). Participants are currently being followed semiannually at the ACHIEVE field sites with final Year 3 study visits scheduled from 2021-22. After their Year 3 visit, all participants randomized to the SA education control group will also be offered the hearing intervention. Final Year 3 results from this original trial will indicate whether hearing intervention (versus a successful aging control intervention) reduces cognitive decline over a 3-year interval after randomization. We now propose to continue following the ACHIEVE cohort for an additional 3 years (i.e., up to Year 6) to determine the long- term effects of hearing intervention (i.e., participants randomized to HI at Year 0) versus successful aging/delayed HI control (i.e., participants randomized to SA at Year 0 and offered HI after their Year 3 visit) on cognitive and brain outcomes. Given that cognitive impairment typically reflects the slow accumulation of pathologic changes, the benefits of HI in slowing this decline may not be fully appreciable within just 3 years. Therefore, this 6-year follow-up of the cohort will allow us to fully evaluate the longer, cumulative impact of HI on older adults. Such findings will complement the main trial results in 2023 and directly inform clinical and policy decisions around the potential use of hearing interventions to reduce the risk of ADRD. This proposed study has the following aims: Aim 1 To determine the long-term effect of HI versus SA/Delayed HI control on rates of the co-primary outcomes of: (a) cognitive decline and (b) incident mild cognitive impairment (MCI)/dementia. Aim 2 To determine the long-term effect of HI versus SA/Delayed HI control on changes in brain MRI measures of: (a) regional...