We study the political ideology of judicial law clerks in the United States, by constructing a novel dataset that combines information on the identity of clerks with a measure of political ideology based on political donations. We then use this data to empirically investigate several important questions about the ideologies of clerks. First, we examine whether clerks tend to share the liberal ideology of other lawyers or the more conservative ideology associated with federal judges and find that clerks tend to be disproportionately liberal. Second, we investigate how the ideology of clerks compares to the ideology of lawyers and find that liberal lawyers are more likely to have clerked than conservatives. Third, we assess whether the ideology of clerks differs based on the level of clerkship and find that the liberal skew becomes less pronounced as the prestige of the clerkship increases. Fourth, we analyze how ideology influences the hiring of clerks and find that the ideology of judges is strongly correlated with the ideology of their clerks.