This article tests multiple hypotheses for the structure of congressional voting on recent immigration reform legislation. In particular, it examines the influence of partisanship, constituencies, and member characteristics. While some accounts have emphasized the cross-cutting nature of immigration policy debates, more recent research finds a growing partisan divide. These votes also provide the opportunity to (1) explore whether a contemporary version of the threat hypothesis -an association between Latino populations and immigration voting -is at work in Congress, and (2) extend the immigration voting literature to the Senate. We find that partisanship is the only consistent factor across votes and chambers. By contrast, district demographics and the personal attributes of members of Congress were not consistently associated with votes. We also found several chamber differences; Latino population was associated with more House than Senate votes, economic competition dynamics may have influenced senators but not representatives, representatives but not senators may have voted with re-election concerns in mind, and the substantive effect of partisanship is larger in the House than in the Senate. Lastly, African-American population was not associated with immigration voting, which stands in some contrast to accounts that emphasize competition between African Americans and Latinos.