Advances in the design of materials for energy storage and conversion (i.e., "energy materials") increasingly rely on understanding the dependence of a material's performance and longevity on three-dimensional characteristics of its microstructure. Three-dimensional imaging techniques permit the direct measurement of microstructural properties that significantly influence material function and durability, such as interface area, tortuosity, triple phase boundary length and local curvature. Furthermore, digital representations of imaged microstructures offer realistic domains for modeling. This article reviews state-of-the-art methods, across a spectrum of length scales ranging from atomic to micron, for three-dimensional microstructural imaging of energy materials. The review concludes with an assessment of the continuing role of three-dimensional imaging in the development of novel materials for energy applications.