Layered double hydroxides (LDHs), a class of anionic clays consisting of brucite-like host layers and interlayer anions, have been widely investigated in the last decade due to their promising applications in many areas such as catalysis, ion separation and adsorption. Owing to the highly tunable composition and uniform distribution of metal cations in the brucite-like layers, as well as the facile exchangeability of intercalated anions, LDHs can be modified and functionalized to form various nanostructures/composites through versatile processes such as anion intercalation and exfoliation, decoration of nanoparticles, self-assembly with other two-dimensional (2D) materials, and controlled growth on conductive supports (e.g., nanowire arrays, nanotubes, 3D foams). In this article, we briefly review the recent advances on both the LDH nanostructures and functionalized composites toward the applications in energy conversion, especially for water oxidation.