ACE-Seniors is designed as a single-site trial of four randomly assigned interventions, Tai Chi exercise, autobiographical writing, both Tai Chi and autobiography (dual intervention), and general health education. Participants are relatively healthy adults aged 70 years or older, who are not regular practitioners of Tai Chi or regular writers. They are without medical or neurological disorders that would substantially limit the ability to participate in study interventions, without dementia or mild cognitive impairment, relatively sedentary, able to walk unassisted, and able to score 4 or better on the Short Physical Performance Battery. Interventions are administered over a 6 month period of time, with similar exposure times among the four groups. The prespecified primary endpoint is derived from a composite neuropsychological measure, based on three tests of executive function and three tests of episodic memory. The planned sample size is 96 (24 per group). Intention-to-treat analysis will include all eligible participants who complete baseline assessments.