Gestures are a common, integral part of communication. Here, we investigate the roles of gesture and speech in explanations, both for communicators and recipients. Communicators explained how to assemble a simple object, using either speech with gestures or gestures alone. Gestures used for explaining included pointing and exhibiting to indicate parts, action models to demonstrate assembly, and gestures used to convey narrative structure. Communicators using gestures alone learned assembly better, making fewer assembly errors than those communicating via speech with gestures. Recipients understood and learned better from gesture-only instructions than from speech-only instructions. Gestures demonstrating action were particularly crucial, suggesting that superiority of gestures to speech may reside, at least in part, in compatibility between gesture and action. (c) 2005 Elsevier Inc. All rights reserved.