Abstract The goal of this article is to review how, when, and why fluency, or processing ease, affects attitudes. The current article first defines fluency and then discusses its direct impact on attitudes, noting that fluency usually makes attitudes more positive and that it does so for a wide array of attitude objects. Mechanisms and moderators of these direct effects are also described. The article then summarizes how fluency can affect attitudes indirectly, through its impact on other judgments (like perceptions of confidence or truth) and on cognitive operations (like information processing). The article ends by highlighting a few areas where additional research is likely to reap impressive benefits.