AIMS: Research shows that the older population increases worldwide, which will likely lead to a rise in the number of people living with age-related disabilities (i.e. hearing and vision difficulties, physical mobility or cognitive ability). However, studies from the Nordic countries have indicated that the likelihood of having disabilities has decreased over time among older adults. This doctoral thesis is based on four studies, which collectively aim to analyze how older adults (aged 75 and above) perceive what constitutes successful aging, estimate the prevalence of hearing and vision impairments in different segments of the older population, examine the importance of cognitive abilities and hearing and vision in the observed declines in disabilities over time among older adults in Sweden and Denmark, and, finally, investigate the longitudinal interplay between sensory function and cognitive abilities among older adults.. METHODS: For Study I, a systematic review was conducted, while for Study II the prevalence of sensory difficulties was estimated. For Study III, the Karlson Holm Breen method was used to estimate the contribution of the cognitive and sensory functions on disability, whereas Study IV applied a cross-lagged panel model to explore the bidirectional relationship between sensory and cognitive functions. For study II, III and IV, data from the Survey of Health, Ageing and Retirement in Europe was used. RESULTS: The findings show that older adults’ own perceptions of successful aging include themes such as life, death, and environmental/systemic influences (Study I). Study II showed that the prevalence of hearing and vision impairments varied among different groups of older adults. Study III found that the decline in the prevalence of disabilities among older adults in Sweden and Denmark could be explained by improved cognition, education, and vision and hearing. Finally, the results from Study IV indicate that no reciprocal effects could be established between sensory functions and cognitive abilities in the short term. DISCUSSION: This thesis highlights the complex relationship between aging and disabilities in Sweden and Denmark and shows various perspectives on what successful aging means for older adults. The findings also reveal significant differences in the prevalence of hearing and vision difficulties among different groups of older adults and show that the prevalence of disabilities has decreased over time in the older population due to improvements in cognition, education, vision, and hearing. These results emphasize the importance of further research on how these factors, along with the use of assistive devices, have contributed to the observed trend. Further research, based on various types of studies and assumptions, is also needed to clarify whether there are any longitudinal associations between cognitive and sensory functions among older adults and, if so, to what extent they can be considered causal.