This paper is based on a presentation made during the Indiana Alzheimer Disease Center's Symposium on Mild Cognitive Impairment on April 19, 2008. The results of the ACTIVE study (Advanced Cognitive Training for Independent and Vital Elderly) were presented at the symposium including review of previously published study findings. The ACTIVE study is a multicenter, randomized, controlled clinical trial that has been examining the long-term effectiveness of cognitive training on enhancing mental abilities (memory, reasoning, and attention) and preserving activities of daily living (managing finances, taking medication, using the telephone, and driving) in older adults. Six centers across the eastern United States enrolled nearly 3000 people initially. Participants underwent detailed assessments of mental and functional ability on multiple occasions over several years of follow-up. ACTIVE has shown positive effects of cognitive training at 5 years post-intervention for basic mental abilities, health-related quality of life, and improved ability to perform instrumental activities of daily living (IADL). A subgroup analysis through 2 years of follow-up suggested that subjects with mild cognitive impairment (MCI) did not benefit from memory training; however, they did benefit, to the same degree as cognitively normal participants, from training in reasoning and speed of processing. This finding suggests that MCI may interfere with a person's ability to benefit from some forms of cognitive enhancement. Limitations of ACTIVE and directions for future research are reviewed.