Diagrams serve multiple purposes, among them to explain. Explaining is not simply showing. Explanations have at least three levels: the specific content, ideally critical junctures in change over time; a causal structure linking the changes; and a narrative structure that aids in organizing the material. Using route instructions and assembly instructions as examples. we analyze the techniques that diagrams, words, and gestures use to convey content, to provide causal links, and to provide a narrative structure. Effective explanations break the action in to major steps, describe, illustrate, or demonstrate action and not just structure, and adopt the user’s perspective. There are striking parallels in the ways these are expressed spontaneously.