When we assess evidence, arguments, and people, we often draw on feelings rather than facts. In this chapter, we describe cognitive fluency—a metacognitive input that shapes forensically relevant judgments such as truth, credibility, and trust. While the legal system strives to keep forensically relevant judgments as accurate and unbiased as possible, the cognitive and social psychological literatures show that changes in the ease of processing information can systematically bias people’s judgments. We explore the consequences for judgments of truth, memory, source credibility, and perceived coherence and consider how cognitive fluency may influence, bias, and distort judge and juror decision making and forensic science communication more generally.