Abstract: The China Spallation Neutron Source (CSNS) is the first such source in China, and the fourth in the world. As an accelerator-based neutron source, CSNS provides intense neutron beams for scientific research and industrial development. The large facility can host hundreds of researchers from university, national labs and industries in physics, chemistry, biology, energy, and material science from all over the world. In this paper we describe the basic principles, historic development, and applications of CSNS.