The 45 and Up Study is a major long term study into healthy ageing, which will provide the first complete picture of the health of people as they move from mid to later life. The Study aims to provide answers to many important health and quality of life questions and will also help governments, health services and policy makers with the future planning of health care services. The 45 and Up Study is now the largest cohort study in Australia, with currently just under 60,000 participants. It’s well on the way to being the largest study of its kind in the Southern Hemisphere. Ultimately, the Study will recruit 250,000 adults aged over 45 in NSW to take part – 10% of the eligible population in NSW. There is no other longitudinal study of this scale in Australia. The 45 and Up Study is taking place in NSW, because of the diversity and size of population in the state. The 45 and Up Study is being implemented by the Sax Institute, which is an independent organisation funded by NSW Health to improve the impact of research on policy and practice. The Study was established in 2003, and launched in 2006. It will be an internationally unique bank of information to enable us to understand healthy ageing and to better plan services and programs for people as they age. Its large size gives the Study power to answer research questions quickly, and also to address a diverse range of research questions, even those relating to uncommon conditions and small population groups. The Study is significant internationally, because it has comprehensive linkages in place – participants have consented to link their Study data with a wide variety of other databases about health and use of health-related services - enabling research that is of direct relevance to health policy. The 45 and Up Study is supported by a broad coalition of funding partners: The Cancer Council NSW; The National Heart Foundation (NSW Division); beyondblue; the national depression initiative; the NSW Department of Ageing Disability and Home Care; and NSW Health. Further financial support is provided by: the MBF Foundation; Macquarie Bank Foundation; Freehills; the Baxter Charitable Foundation and Alma Hazel Eddy Trust (both managed by Perpetual Ltd); and Trust. The Study has ethical approval from the University of NSW Human Research Ethics Committee. It is also overseen by a Scientific Advisory Committee and a Community and Ethical Oversight Committee. Participants in the 45 and Up Study provide information on their health via a baseline questionnaire that is mailed to people in the target age range, who are selected at random from the Medicare Australia enrolment database (though Medicare has no other role in the Study). Individuals resident in rural areas and those aged over 80 are over-sampled to ensure adequate statistical power amongst these groups. The 45 and Up Study is an open resource which researchers and policy-makers can apply to use. To date there have been 20 applications to use data from the Study by a broad range of groups and projects.