With falling birth rates and increasing life expectancy we are an ageing society. 20% of boys and 25% of girls born in 2019 are expected to reach their 100th birthday. This would be good news if it were not for the fact that healthy life span has not kept pace with increasing longevity and now on average adults spend the last 15-20 years of life in ill health. Frailty is a major component of ill health in old age and refers to an enhanced vulnerability to stressors, such as falls, surgery or infections, which was demonstrated clearly in the mortality data for the COVID19 pandemic. The transition from robust health to frailty is a critical factor in the loss of independence and places increased pressure on health and social care. All of this has led governments to prioritise the enhancement of healthspan. The Doctorate Network on UnderstandiNg fraIlty tOwards a future of healthy ageiNg (UNION) is a multi-partner joint doctoral research training network with the overall aims of educating 13 Early Stage Researchers (DCs), advancing the current understanding of frailty, and providing innovative solutions on how healthy ageing can be achieved. UNION brings together world leaders in a range of relevant disciplines (frailty, ageing biology and ageing medicine, inflammation, immunosenescence, immunometabolism, stem cell biology) with state-of-the art technologies including mass spectrometry metabolomics, advanced imaging, artificial intelligence, CRISPR-CAS9 libraries, SPECTRA 35-colour flow cytometry, global and conditional knockout mice. This technological excellence is applied to the clinical situation through unique longitudinal human ageing and frailty cohorts, longitudinal assessment of age-related multimorbidity in animal models and innovative multidimensional frailty indices in humans. Together this integrated activity will provide the highest quality training and research environment in our rapidly ageing society.