Localized-surface-plasmonic (LSP) nanostructures can efficiently collect light propagating in free space and converge it onto nanoscale “hot spots” in the near-field region, enabling efficient excitation of molecules. Conversely, spectral information about molecules in the hot spots can be “broadcast” to the far field. This process is accompanied by the enhancement of light absorption, radiation, scattering, light force, resonance migration, and photothermal effects. The rich phenomena associated with LSP nanostructures have resulted in a series of applications in the field of sensing, including surface-enhanced infrared-absorption spectroscopy, surface Raman spectroscopy, surface fluorescence spectroscopy, LSP refractive-index sensors, nano-optical tweezers, and LSP matrix-assisted laser desorption/ionization. However, the complexity of LSP behavior also makes it difficult for researchers to understand the mechanisms and applications of this field. For this reason, we review and sort out all types of LSP sensors from the perspectives of both theory and applications. For example, the eigenmode theory based on the quasi-static approximation provides a unified analytical theoretical framework for all kinds of LSP-related phenomena. We provide a brief review of the progress and challenges of various related applications, including Raman scattering, infrared absorption, fluorescence, refractive-index sensing, and laser desorption/ionization, to provide a clear and concise overview for researchers in this field.