Deep-red light has significant application value in various fields, including biomedicine, plant cultivation, and displays. The development of high-efficiency deep-red luminescent materials is therefore of great importance. Semiconductor nanocrystals have been extensively studied as novel luminescent materials due to their wavelength tunability, narrow emission linewidth, and high luminescence efficiency. However, the advancement of deep-red nanocrystals has lagged behind that of red, green, and blue nanocrystals, primarily due to material selection limitations. This review summarizes the recent progress in the synthesis of deep-red nanocrystals based on their material composition, including II-VI, III-V, I-III-VI, and perovskite nanocrystals.