The Canadian Longitudinal Study on Aging is following 50,000 men and women aged 45–85, every three years for at least 20 years. Of the total, 20,000 (Tracking participants) are randomly selected within age/sex strata in each province, and 30,000 (Comprehensive participants) are randomly selected within age/sex strata from within 25–50 km of 11 sites across the country (Victoria, Vancouver, Surrey, Calgary, Winnipeg, Ottawa, Hamilton, Montreal, Sherbrooke, Halifax, and St. Johns). Data collection methods include telephone and face-to-face interviews, physical assessments, biological samples, and linkage to administrative databases. Initiated in 2010, the second wave of data collection is currently underway. The CLSA has engaged in a number of “firsts” in Canada. In this presentation we will highlight the study design and content, sampling, recruitment, baseline data collection, and ascertainment of health outcomes. Ethical legal and social issues, as well as accommodation strategies to improve retention in future waves will be presented.