Crystal structure and composition are strongly correlated to materials' properties and functionalities. In this section, we first introduce the crystal structures and corresponding properties 2D ternary chalcogenides have been extensively studied by researchers from materials science and nanotechnology because of their unique structures, novel chemical and physical properties, and great potential in nanoscale device applications. With the addition of a third element, these 2D ternary chalcogenides are anticipated to be more appealing because of the stoichiometric variation and synergistic effect compared to their binary counterparts. The novel properties of 2D ternary chalcogenides have endowed various applications in electronics, optoelectronics, biosensors, and catalysis. Here, a summary is given of the latest research progress of 2D ternary chalcogenides from the aspects of preparation, characterization, and application. The article is concluded with a screening of the existing challenges and an outlook for these rising 2D ternary materials.