Raman spectroscopy is a powerful optical spectroscopic method

of chemical analysis with a wide field of applications, ranging

from pharmaceutical and biomedical studies to art and archaeology

[1-3]. These are based on the fingerprint-like information that

it provides by analyzing molecular vibrations. Its capabilities are

however outperformed in several applications where a very high

sensitivity is required, for example, for detecting molecular trace

amounts, mainly due to the very low efficiency of the Raman

scattering process. Surface-enhanced Raman spectroscopy (SERS)

provides the means for improving the sensitivity by amplifying the

original Raman scattering intensity for several up to ten orders of

magnitude. It was more than 30 years ago that an enhanced Raman

signal was observed from molecules adsorbed at roughened silver

electrode surfaces [4, 5]. Since then a huge amount of workwas done

in order to understand its multiple-faceted aspects, and develop

SERS applications, this work being still in progress. Although a big

part of the fundamentals of the technique had been established

in the 1980s, important contributions to the advancements have

been achieved during recent years, in which we have witnessed

an intense blooming in the development of SERS, mainly in direct

relationship with the rising field of plasmonics. In turn, this latter

was boosted by the rapid evolution of nanotechnology in general,

which provided nanofabrication and characterization methods of

continuously increasing performance. Current challenges addressed

in the last years, and ongoing, are both on controlling the fabrication

of SERS substrates with nanoscale precision and on furthering the

current understanding of the details of SERS effects.