Abstract: Do legislators and lobbyists trade favors? This study uses uncommon data sources and plagiarism software to detect a rarely observed relationship between interest group lobbyists and sitting Members of Congress. Comparison of letters to a Senate committee written by lobby groups to legislative amendments introduced by committee members reveals similar and even identical language, providing compelling evidence that groups persuaded legislators to introduce amendments valued by the group. Moreover, the analysis suggests that these language matches are more likely when the requesting lobby group hosts a fundraising event for the senator. The results hold while controlling for ideological agreement between the senator and the group, the group’s campaign contributions to the senator, and the group’s lobbying expenditures, annual revenue, and home-state connections.