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The Zurich Longitudinal Study on Cognitive Aging (ZULU) is an ongoing longitudinal study on the structure and development of cognition in old age. At the first assessment, the N = 364 participants had an average age of 73 years (age range: 65-80 years), and 46% were female. In total, a battery of 14 cognitive tests, including five consecutive verbal learning trials, were administered and adequately described by a measurement model of six first-order factors (processing speed, working memory, reasoning, learning, memory, and verbal knowledge) and one second-order factor of general cognitive ability. The cross-sectional age relations of the six cognitive abilities were, apart from processing speed and verbal knowledge, mediated by the general cognitive ability factor. From a conceptual perspective, these results imply that cognitive aging is not a completely uniform process driven by a single causal variable.