The fundamental mechanism of SERS (Surface ehanced Raman spectroscope), such as electromagnetic and chemical effect, as well as the synthesis of SERS tags with high enhancement, which will be applied in single molecule detection and single cell imaging, were discussed. For applications, SERS nanoparticle tags have been developed based on the use of embedded reporter molecules and a silica or polymer encapsulation layer. The SERS nanoparticle tags are capable of providing detailed spectroscopic information. These properties have raised new opportunities for multiplexed molecular diagnosis and in vivo Raman spectroscopy and imaging.Cited