Concerns about loneliness and social isolation are growing more than ever. With the COVID-19 pandemic entering its second year, there are fears that the toll on loneliness could have consequences long after the virus recedes. This study offers a comparative overview of the incidence and determinants of loneliness and social isolation in Europe in the pre-COVID-19 period. The empirical results indicate that 8.6% of the adult population in Europe suffer from frequent loneliness and 20.8% from social isolation, with eastern Europe recording the highest prevalence of both phenomena. Trends over time do not indicate any change in the incidence of social isolation following the widespread adoption of social media networks from 2010 onwards. The empirical analysis shows that favourable economic circumstances protect against loneliness and social isolation, while living alone and poor health constitute important loneliness risk factors. Although social isolation increases with age, the elderly do not report more frequent feelings of loneliness than other age groups, all other things being equal. The relative contributions of the different objective circumstances included in the empirical analysis — demographic characteristics, economic conditions, living arrangements, health status, religious beliefs and geographical location — to chronic loneliness and social isolation vary substantially.