Halide perovskites are expected to be widely used in light-emitting diodes (LEDs) due to their excellent optoelectronic properties, such as high luminous efficiency, controllability of luminescence wavelength, and wide color gamut. However, because the exciton binding energy of 3D halide perovskite films is relatively low (≈150 meV), various techniques have been applied to increase the exciton binding energy and thereby improve the performance of devices. Among them, 0D halide perovskite nanocrystals (NCs) are widely used because the low-dimensional perovskite effectively confines the excitons in NCs. In particular, perovskite NCs facilitate color tuning with quantum confinement by controlling the size. Herein, it is aimed to provide an overview of various approaches for synthesizing perovskite NCs and post-treatment methods to achieve high-efficiency LEDs.