People gesture when they speak, especially when speaking is difficult. People are more likely to gesture when their speech is disfluent or when they are about to utter a low probability word. Why? According to an influential answer to this question, people gesture when speaking is difficult because gestures facilitate speech production – serving a cognitive function for the speaker. In Study 1, I aimed to conceptually replicate the finding that preventing gestures makes speakers more disfluent – the primary finding that has been interpreted as evidence for this influential hypothesis. Contrary to long-held beliefs, I showed that there is, in fact, no support for the claim that preventing gestures impairs speaking – in a large dataset and re-examining five decades of empirical evidence cited for this claim. If gestures do not help speech production, why then are people more likely to gesture when speaking is difficult? To answer this question, I proposed and tested an alternative explanation. Gesturing when speaking is difficult may not be a mere symptom of speaking difficulties. And gesturing may not be produced to help speakers resolve these difficulties, either. Instead, gesturing when speaking is difficult may be communicatively motivated. In Study 2, I showed that speakers are more likely to gesture when they are disfluent because gestures serve as a pragmatic signal to the listener commenting on experiencing problems with speaking. When gestures were not visible and therefore could not serve as a pragmatic signal to the listener, they were not more likely to occur during disfluent speech than fluent speech. In Study 3, I showed that speakers are more likely to gesture before they are about to utter a low probability word because gestures signal and depict hard to predict words for the listener. When gestures were not visible and could not serve as a communicative signal to the listener, they were not more likely to occur before uttering a low probability word than a high probability word. Together, these three studies motivate a revision to theories of why people gesture. People gesture when speaking is difficult, because gestures provide a communicative signal to the listener, commenting on the process of speaking or the content of upcoming words.