In-space electric propulsion technologies have advanced significantly in the last decade, while there has been increasing interest in economical propulsion systems with growing demand for commercial and scientific applications using small spacecraft platforms. Electrostatic propulsion, in particular, offers advantages over other propulsion systems in various aspects, including long operational lifetime, high specific impulse, and light weight. However, electric propulsion systems are subject to drawbacks such as system complexity and wall erosion, which represent obstacles toward miniaturization to be utilized for small spacecraft. New ideas are continuously explored to overcome such challenges and improve the performance. This article presents a comprehensive review of electrostatic propulsion systems, with particular focus on Gridded Ion Engine (GIE), Hall Effect Thruster (HET), and Cusped Field Thruster (CFT) systems, with respect to their operational principles, applications, and characteristics. State-of-the-art technologies and novel concepts are discussed including research efforts for miniaturization, along with the latest available data of their performance and features. While GIE and HET are mature and well understood, the power consumption of miniaturized thrusters is relatively high, leaving room for improvement toward practical application. CFT, on the other hand, features appreciable performance even in miniaturized form, offering promise to serve for small spacecraft platforms.