Аннотация:We argue that cultural threat, stressed in recent studies of anti‐immigrant sentiment, is properly measured in the U.S. case as “assimilationist threat”: a resentful perception that immigrants are failing to adopt the cultural norms and lifestyle of their new homeland. We explore the meaning and form of assimilationist threat in the minds of Americans through an analysis of four focus groups, two in Los Angeles, CA, and two in Columbus, OH. Using information from the focus groups, we develop and test a set of survey questions covering three dimensions of immigrants’ commitment to their new country: language, productivity, and citizenship. We produce a summary scale of assimilationist threat that can be used by other researchers seeking to understand the causes and consequences of anti‐immigrant sentiment.