Branched nanowires (or referred as nanotrees, nanoforests) with tunable 3D morphology, homo or heterogeneous junction, and interface electronic alignment represent a unique system for applications in energy conversion and storage devices. Compared with OD nanoparticles and 1D nanowires, 3D branched nanowires possess advantages including structural hierarchy, high surface areas and direct electron transport pathways. Therefore, branched nanowires are under the focus of recent research on energy materials. In this Review, the synthesis of a wide variety of branched nanostructures is summarized. The methods cover vapour phase, solution phase, and their combinations. As the main part of this Review, the latest results on the energy applications of branched nanowires in photovoltaics, photocatalysis, photoelectrochemical water splitting, supercapacitors and Li ion batteries are highlighted, and the benefits of the 3D branch structure is discussed. (c) 2012 Elsevier Ltd. All rights reserved.