Age-related declines in cognitive processing are well documented and may contribute to limitations performing daily living tasks as people age. The purpose of this dissertation was to examine the relationships among cognitive processing, physical function, and disability in older adults. Three studies were organized into three distinct manuscripts. In this dissertation, we use the term cognitive processing to refer to performance on measures of attention and processing speed. The objective of the first study was to examine the direct and indirect effects of cognitive processing on physical function and disability. The second study examined: (1) the predictive relationship of cognitive processing to changes in physical function and disability, and (2) the association of change in cognitive processing to change in physical function and disability. The purpose of the third was to explore the relationship of cognitive processing to self-reported disability measured as dependence and measured as difficulty. The combined results of all three experiments confirmed that cognitive processing is associated with both concurrent and future levels of physical function and disability in older adults. The relationship between cognitive processing and disability is primarily mediated by physical function, such that poor cognitive processing is associated with lower levels of physical function and indirectly with higher levels of disability. Poor baseline cognitive processing is also predictive of decreased balance and disability one year later. The relationship of cognitive processing with disability appears to be most robust when iv disability is defined as dependence. These results illustrate the complex relationship of cognitive processing to physical function and disability in older adults.