Metal nanoparticles have recently emerged as ubiquitous surface-enhanced Raman scattering (SERS) agents for nano-imaging and nano-analysis. These applications make use of the unique optical properties of metal nanoparticles to enhance the efficiency of Raman scattering, whereas the small size of the nanoparticles localizes the enhanced Raman scattering at the nanoscale. In this perspective, we review the recent progress in SERS nano-imaging and nano-spectroscopy using metal nanoparticles applied especially to biological samples and nanomaterials. For biosamples, the highly sensitive molecular SERS detection capability of metal nanoparticles is used to analyze intracellular molecules. For analysis of nanomaterials, an innovative approach called tip-enhanced Raman scattering (TERS) microscopy, where metal nanoparticles are used with an AFM cantilever, has proven to be extremely powerful for nano-imaging. The precise control and analysis of the interaction between the metal and the sample are thus the key to overcome the limitations of current microscopic and spectroscopic techniques, and to guide future developments.