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We discuss a nanowire and nanotube formation mechanism in which axial screw dislocations provide self-perpetuating steps to enable one-dimensional (1D) crystal growth, unlike previously understood vapor−liquid−solid (VLS) or analogous metal-catalyzed growth. We initially found this mechanism in hierarchical pine tree PbS nanowires with helically rotating branches. We further applied it to ZnO, demonstrating that screw dislocations can drive the spontaneous formation of nanotubes, and used classical crystal growth theory to confirm that their anisotropic 1D growth is driven by dislocations. Dislocation-driven growth should be general to many materials grown in vapor or solution and is underappreciated. It will create a new dimension in the rational synthesis of nanomaterials. The resulting complex hierarchical nanostructures can be useful for solar energy conversion, and our understanding will allow large …