What are the rules that make branches? Why does a lightning bolt seek many routes from heaven to earth, or a crack begin to wander and divide? Branching forms find a compromise between disorder and determinism: they hint at a new and peculiar geometry. Yet sometimes order reasserts itself, as when the arms of snowflakes insist on their hexagonality. And if branches reunite, the loops form a web that offers many routes to the same destination. Navigation and dissemination on such networks then depends on the pattern of connections.