It is widely recognised that the formal institutional context affects firm ownership concentration. However, the impact of the informal institutional context has received less research attention. Drawing from institutional theory, we tested our hypothesis that both the formal and informal (cultural) institutional contexts simultaneously influence firm ownership concentration. Based on a firm-level database of the largest 600 listed companies in 19 European countries for the period 2009–2015, we found that both formal and informal institutional contexts, considered independently from each other, affect the level of firm ownership concentration. However, when these institutional contexts are considered together, the significance of the formal institutional context's effect on ownership concentration disappears while the informal (cultural) institutional context remains significant. Specifically, our findings indicate that high power distance, collectivism, uncertainty avoidance, restraint, and short-term orientation favour firm ownership concentration. Overall, our findings demonstrate that the diversity in European cultures explains firms' different levels of ownership concentration across European firms, signalling that the European Union's efforts towards a common regulatory frame may not necessarily lead to a convergence of European firms' ownership structures and, consequently, of corporate governance practices.