Although cities are thought of as environments conducive to collective mobilisation, we know less about the collective processes by which marginal social groups take advantage of these environments to advance their claims. This article uses the concept of bridging social capital to explain the process by which immigrants living in cities with high diversity mobilise. It introduces the concept of bridging environments to show how city context shapes the collective mobilisation of immigrants. Mobilisation is contingent on the bridging environments with which immigrants can connect within the cities in which they settle. This argument is exemplified by a comparative analysis of the collective mobilisation of Ecuadorian immigrants in New York City and Madrid. This research contributes to how city context matters for the mobilisation and political incorporation of immigrants in liberal democracies.