Abstract <p>This comprehensive review presents the main characteristics of plasmonic nanoparticles (PNPs), especially consisting of noble metal nanoparticles (NMNPs) such as silver (Ag), gold (Au), and palladium (Pd), and brief information on their synthesis methods. The physical and chemical properties of the metal NPs are described, with a particular focus on the optically variable properties (surface plasmon resonance-based properties) and surface-enhanced Raman scattering of plasmonic materials. Plasmonic NPs have attracted particular attention due to their strong optical, electrical, biological, and catalytic effects, which are accompanied by surface plasmon resonance characteristics of plasmonic NPs. Their assemblies enable fine-tuning of these effects with unprecedented dynamic range. In turn, the uniquely high polarizability of plasmonic nanostructures and related optical effects exemplified by surface-enhanced Raman scattering and red–blue color changes give rise to their application to bio-sensing. In addition, this review covers ways to achieve advances by utilizing their properties in catalytic, sensing, and biological studies. These descriptions will help researchers new to nanomaterials for catalytic and biomedical diagnosis to understand the related knowledge easily. They will also help researchers involved in the biomedical field to learn about the latest research trends.</p>