Older adults exhibit decreased speed and accuracy in naming objects, more slips of the tongue, more pauses in speech, and more tip-of-the-tongue experiences, in which one cannot produce a word even though there is a vivid sense of knowing it. Importantly, older adults rank these experiences as a frustrating, embarrassing, and frequent memory problem. While word retrieval failures reflect a common aspect of aging that affects the vast majority of older individuals, the neural bases of language production in healthy aging has received little attention. Research suggests that these failures result from a phonological deficit. Indeed, results from the prior funding period demonstrated significant age-related decline and weakened brain-behavior links underlying phonological aspects of language production. However, we have only begun to examine the causal factors that contribute to word retrieval difficulty. Thus, the overarching goal of the present proposal is to use behavioral measures, functional magnetic resonance imaging (fMRI), and diffusion tensor imaging (DTI) to investigate the causal factors that contribute to age-related declines in word retrieval. We propose a series of 5 experiments that will investigate the influence of lexical and behavioral factors that contribute to word retrieval difficulty to advance theoretical accounts of age-related differences in language production. The multimodal approach will allow us to examine the relations between cognitive abilities, language production, and neural factors such as white matter integrity and functional activation in healthy aging. Our long-term goal is to advance theoretical accounts of age-related differences in language production. Our work is guided by the Transmission Deficit Theory (TDT), which proposes that age weakens connections within the language system, and that age-related transmission deficits disrupt word production more than word comprehension because of differences between the architecture of phonological and semantic representations. This research will improve the current scientific understanding of age-related changes in language, and provide a characterization of the neural factors that contribute to cognitive decline. These results will provide essential information for differentiating normal age-related changes in language from the effects of disease, forge advances in our theoretical conceptualization of age- related differences in language, and provide insight into rehabilitative therapies for cognitive decline in both healthy aging and clinical patients.