The rapid development and further modularization of miniaturized and self-powered electronic systems have substantially stimulated the urgent demand for microscale electrochemical energy storage devices, e.g., micro-batteries (MBs) and micro-supercapacitors (MSCs). Recently, planar MBs and MSCs, composed of isolated thin-film microelectrodes with extremely minimized ionic diffusion path and even free of separator on a single substrate, are becoming particularly attractive because they can be directly integrated with microelectronic devices on the same side of one single substrate to act as a stand-alone microsized power source or complement miniaturized energy harvesting units. This progress report highlights the development and recent advances of planar MBs and MSCs from the fundamentals and design principle to the fabrication methods of two-dimensional (2D) and three-dimensional (3D) planar microdevices in both in-plane and stacked geometries, and provides a comprehensive analysis of the primary aspects of electrode materials, electrolyte, device architecture, and microfabrication techniques that eventually affect the performance metrics of microscale energy storage devices. The technical challenges and prospective solutions for high-energy-density planar MBs and MSCs with multi-functionalities are proposed.