Mark Twain’s distaste for anti-Semitism was well-known. He had published a searing exposé of anti-Semitism in the Austro-Hungarian empire. He had minced no words denouncing pogroms in Russia and had been a featured speaker at a benefit for Russian Jews. He had condemned French anti-Semitism in the Dreyfus Affair on numerous occasions. In a widely-read essay called “Concerning the Jews” he had provided his own analysis of the roots of anti-Semitism. And when his daughter decided to marry a Russian Jewish pianist and conductor, Twain warmly welcomed the son-in-law into the family. So how can it be that some of Twain’s comments from “Concerning the Jews” regularly get quoted with approval today on white supremacist, neo-Nazi, and other anti-Semitic websites and blogs? This essay draws on Mark Twain’s writings and biography; on nineteenth- and early twentieth-century social, cultural, and political history; and on scholarship on the history of anti-Semitism and racism to explore some answers to this question. It endeavors to complicate our understanding of Mark Twain’s attitudes—his astute insights and his embarrassing blind spots, his lucidity on the one hand, and his myopia on the other.