This perspective presents an overview of single-molecule surface-enhanced Raman scattering (sm-SERS). Our overview is organized as a brief theoretical background, discussion of the factors that enhance SERS, various experimental preparations for inserting a single molecule in a hot spot, recent sm-SERS experiments, and a perspective. Although, there have been numerous review papers on sm-SERS, we mainly concentrated on the logical development of sm-SERS on the basis of the fundamental concepts and their physical significance, so that readers outside this field can understand the motivation and the underlying physics when describing current sm-SERS measurements. Indeed, understanding such current sm-SERS experiments conducted by representative groups would be very helpful for readers to answer for themselves the fundamental and practical questions surrounding sm-SERS: (1) what information can sm-SERS provide? (2) Which factors based on the SERS mechanism should be considered to significantly amplify the SERS signal? (3) What kinds of related microscopy techniques could be combined with sm-SERS to attain more meaningful results? (4) Which statistical approaches can be used and how they can be applied to properly analyze sm-SERS data? We hope that this review article can help readers answer these questions.