Large electromagnetic field (E) enhancement enabling ultra-sensitive surface enhanced Raman spectroscopy (SERS) has been realized within a gap region of noble metallic nanostructures serving as a plasmonic nanoantenna. However, despite 30+ years of extensive research, SERS is yet to be realized as a routine analytical tool partly due to our inability to controllably fabricate clean and reproducible nano-gap sizes and our limited understanding of underlying enhancement mechanisms. This talk will cover three general topics on SERS. First, I will discuss our current understanding of SERS and its underlying mechanisms. Second, I will present recent progresses in nanofabrication leading to improved understanding of the gap-dependent electromagnetic field enhancement and SERS. In particular, I report the use of Ag@SiO2 core-shell nanoparticles for probing spatial distribution of the E field enhancement via SERS and the use of novel suspended gold bowtie nanoantenna arrays capable of generating plasmonic nanocavities that enable reproducible, single-molecule Raman spectroscopy. With these idealized bowtie arrays, we reveal an anomalously weak power law dependence of E on the gap size and provide a definitive proof of the existence of the collective photonic effect. Finally, I will provide future research perspectives on SERS and its potential in biological, environmental, and security applications.