The article reviews the fundamental physics of surface-plasmon excitations at metal/dielectric interfaces, focusing on their potential for localizing electromagnetic energy in one, two, and three dimensions. It discusses the localization of plasmon resonances in metallic nanoparticles, both for single particles and ensembles, and the enhancement of Raman scattering and nonlinear processes. The properties of interface plasmons propagating along flat boundaries of thin metallic films are surveyed, including their applications in waveguiding along patterned films, stripes, and nanowires. The interactions between plasmonic structures and optically active media are also explored. The review highlights the development of nanofabrication techniques and modern characterization tools that have advanced research in this field, enabling the creation of subwavelength optical devices and the miniaturization of optical components.The article reviews the fundamental physics of surface-plasmon excitations at metal/dielectric interfaces, focusing on their potential for localizing electromagnetic energy in one, two, and three dimensions. It discusses the localization of plasmon resonances in metallic nanoparticles, both for single particles and ensembles, and the enhancement of Raman scattering and nonlinear processes. The properties of interface plasmons propagating along flat boundaries of thin metallic films are surveyed, including their applications in waveguiding along patterned films, stripes, and nanowires. The interactions between plasmonic structures and optically active media are also explored. The review highlights the development of nanofabrication techniques and modern characterization tools that have advanced research in this field, enabling the creation of subwavelength optical devices and the miniaturization of optical components.