Abstract: Synchrotron radiation light sources based on electron storage rings are the most widely used high-performance X-ray sources in the past 20th century, and have become important tools for frontier research in the fields of physics, chemistry, energy and environment, biomedical science, and advanced materials. In the 21st century, the foremost ring-based light source is the fourth-generation synchrotron radiation light source (4GLS). It generally adopts a compact multi-bend achromat lattice to achieve ultralow electron beam emittance that approaches the diffraction limit of X-rays, thus enabling an increase in the brilliance of the synchrotron radiation by 2—3 orders of magnitude compared to existing third-generation sources. This article will focus on the key accelerator physics and technology issues, as well as the current status, of 4GLSs around the world.