The population undergoing surgery is getting older. Surgery poses a higher risk in older people compared to younger people. Older patients may have specific health threats, but being old does not necessarily mean one has a decreased health status. A substantial part of the older population is still living active and healthy. Biological age seems to be a more important risk factor for negative health outcomes than chronological age. It is therefore essential to identify older people who are at risk of adverse health outcomes after surgery, to correct modifiable risk factors and to adapt their care if necessary.The aim of this thesis was to study how, through better perioperative care, we can improve postoperative outcomes for older patients....