Since 2005, the 45 and Up Study has been following over a quarter of a million people to understand how Australians are ageing and the factors that promote good health and wellbeing. The baseline data sweep involved over 36,000 participants. Of this baseline cohort, 52% of participants were female, ranging in age from 45 to 101 years, with a mean age of 64.1 years for men and 61.3 years for women. The data that is collected for the 45 and Up Study include a baseline questionnaire, 5-yearly repeat questionnaires, linkage to routinely collected health and government data, biological samples, and more intensive measures from sub-studies conducted within the cohort. As of August 2024, there are more than 250,000 participants in the cohort.