Metal-trihalide perovskite quantum dots combine the unique semiconducting properties of bulk perovskites with the controllable exciton dynamics benefiting from the quantum confinement effect. Composition- and size-adjustable electronic and optical properties of perovskites convert into a variety of applications. Here, we start from a brief introduction to perovskite quantum dots, followed by a detailed description of the synthesis methods and surface modification/passivation strategies of these nano-sized particles. Then, we review the applications of perovskite quantum dots including light-emitting diodes, photovoltaics, catalysis, sensing, bioimaging, and lasers. Finally, we develop outlooks for promising futures toward the commercial application of perovskite quantum dots.