The relationship between police and ethnic minorities has been the subject ofincreasing interest in many Western societies in recent years. We examine firstgeneration immigrants’ trust in the police in Europe from a comparative andlongitudinal perspective. Based on roughly 20,000 immigrants observed in 22countries over 13 years in the European Social Survey, results show thatinitially high levels of trust in the police among immigrants tend to erodewith the length of their stay in the host country. We show that twosimultaneous processes drive this pattern: a fading reference effect(downward assimilation) and an increasing discrimination effect. Crossnational comparisons show that, on average, immigrants in countries withmore police trust the police less. However, there is no effect of police sizewithin countries, mostly because police numbers hardly change over time.We discuss implications for future research and policy development based onour findings.