After decades of relatively high inflows of foreign nationals, immigration is now at the center of substantial political divisions in most European countries and has been implicated in one of the most vexing developments in European politics, the rise of the xenophobic right. However, it is not clear whether high levels of immigration actually do cause a public backlash, or whether publics become habituated to, and supportive of, immigration. This study tests these backlash and habituation theories using novel measures of immigration mood and immigration concern produced by combining over 4,000 opinion datapoints across twenty-nine years and thirty countries. The authors find evidence of a public backlash in the short to medium run, where mood turns negative and concern about immigration rises. Yet the study also finds evidence of a longer-run process of habituation that cancels out the backlash effect within one (concern) to three (mood) decades.