What explains variation in citizens’ belief in US-related conspiracy theories in the Arab Middle East? Some scholars have argued that anti-US sentiment or individual-level characteristics identified in other contexts can explain the Arab public’s belief in these conspiracy theories; others have argued that citizens of autocracies are more likely to trust such theories. We explore these claims using a conjoint experiment with representative samples from 10 Arab countries. We find that extant explanations do not do a good job of describing the variation we observe—e.g., correlation with anti-US sentiment depends on the conspiracy theory, and belief in these conspiracy theories is not more common in more authoritarian regimes. Instead, we find Sunni-Shia sectarianism and exposure to foreign intervention in violent conflict to be the dominant factors explaining trust in US-related conspiracy theories in the Arab Middle East.