Continued growth in older adults' computer and internet use has led to the need to better assess their competencies and skills. The aim of the current study was to expand on this literature by examining sources of individual differences in older adults' computer and internet proficiency. Ninety-seven adults ranging in age from 60 to 95 completed the Computer Proficiency Questionnaire (CPQ) along with a battery that measured demographic information, socio-emotional variables such as sense of control and affect, and cognitive abilities such as reasoning and speed of processing. Hierarchical regression analyses examined the predictors of CPQ Total score as well as the three CPQ subscales (e.g., Internet and Email Use, Communication and Calendaring, and Computer Basic). Age, education, affect, sense of control, inductive reasoning, perceptual speed, and psychomotor speed were associated with at least one domain of computer proficiency. Positive affect uniquely predicted Communication and Calendaring. While sense of control, inductive reasoning, and psychomotor speed uniquely predicted Computer Basic. Discussion focuses on implications for CPQ use and computer proficiency training in older adults.