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In this article, we consider how the advent of functional neu-roimaging has either confirmed or changed cognitive theories of the aging mind that had been initially developed from behavioral findings and structural brain imaging. This issue of how functional imaging impacted theories of cognitive aging is particularly interesting because cognitive aging, by its very nature, is a neurobiological event, so it stands to reason that new findings about how the brain functions might change views of how cognitive mechanisms function and differ with age. Inherent in this entire discussion is recognition that even behaviorally derived theories of cognitive aging have often considered underlying brain structures, although relatively little attention has been paid to neural function until the advent of functional imaging. Theories of cognitive aging generally agree on the behav-ioral phenomena to be explained. A vast literature shows that as adults age, many domains of cognitive function decline, including speed of processing, working memory, long-term memory, and reasoning (Hertzog, Dixon, Hultsch, & Mac-Donald, 2003; Park & Reuter-Lorenz, 2009; Salthouse, 1996), all of which decline at similar rates (Park et al., 1996). In addition, some domains of cognitive function are preserved with age, including verbal ability (Park et al., 1996), implicit or procedural memory (Howard, 1988), and prospective mem-ory in naturalistic settings (Henry, MacLeod, Phillips, & Crawford, 2004). Finally, it is well-recognized that as cogni-tive tasks become more demanding, age differences in perfor-mance often become larger (Myerson, Hale, Wagstaff, Poon, & Smith, 1990). Most behavioral theories of cognitive func-tion address all of these findings. We will selectively review three major theoretical accounts of cognitive aging that focus on different behavioral mecha-nisms as the basis for cognitive aging, and have served as the conceptual basis for much research. We also briefly describe behavioral and structural imaging data that have provided sup-port for the theories. The three theories we discuss are (a) speed of processing (Salthouse, 1996), (b) limited cognitiv