Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other small autonomous devices. Although there are few examples to date of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. This overview highlights the various architectures proposed for 3D batteries, the advances made in the fabrication of components designed for these devices, and the remaining technical challenges. Efforts directed at establishing design rules for 3D architectures and modeling are providing insight concerning the energy density and current uniformity achievable with these architectures. The significant progress made on the fabrication of electrodes and electrolytes designed for 3D batteries is an indication that a number of these battery architectures will be successfully demonstrated within the next few years.