<p>The sound scattering layer (SSL) is a widespread acoustic characteristic in the global ocean, primarily formed by densely distributed zooplankton and small pelagic fish. As an important component of the marine ecosystem, the SSL plays a crucial role in vertical energy transfer, carbon flux, and food web interactions. Diel vertical migration (DVM) is the primary behavioral characteristic of the SSL, driven by a combination of environmental and biological factors, including illumination, water temperature, dissolved oxygen concentrations, food availability, and predation pressure. However, due to limitations in long-term observation capacity, the accumulation of acoustic data, and differences in regional research priorities, the depth of understanding of SSLs varies among different marine regions. This review systematically examines the composition, classification, and DVM characteristics of SSLs, with a particular focus on their research status in the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the polar seas, and the coastal ocean of China. The knowledge of survey status, biological composition, distribution patterns, and DVM behaviors in these regions provides a scientific foundation for advancing the understanding of SSL dynamics. It also supports the sustainable development and management of fishery resources under climate and marine environmental change.</p>