A growing number of people are living with several long-term health conditions like diabetes, heart disease, depression or dementia. We call this multiple long-term condition multi-morbidity (MLTC-M). Many things throughout a person’s life influence the chances of developing health conditions. This includes their biology (e.g. age, ethnicity), things that happen to them (e.g. infections, accidents), behaviours (e.g. smoking, diet) and broader experiences (e.g. the environment people grew up in, their education, work, income). People from more disadvantaged backgrounds and/or certain ethnicities are more likely to develop MLTC-M and to develop it earlier. The impact (or ‘burden’) of MLTC-M, and the order that people develop conditions, also vary.