Although porous silicon (pSi) was first obtained in the mid-20th century, considerable interest in this material arose much later, due to the discovery of its room-temperature photoluminescence (PL). In the 1990s, most studies on pSi were focused on the analysis and explanation of its photoluminescent and electroluminescent characteristics and their potential practical applications. The latest advances in pSi research are related to its biocompatibility and biomedical applications. The discovery of singlet oxygen generation by pSi through nonradiative transfer of photoexcitation energy has opened new prospects for photodynamic therapy in vivo, and the discovery of laser desorption/ionization on pSi has paved the way for advanced approaches in mass-spectrometry. In this study, the main photophysical properties of pSi are reviewed, and a wide range of photo-processes characteristic of pSi and their practical implications are analyzed in terms of the general principles of energy and charge transfer. Special attention is paid to the possible applications of pSi and pSi-based nanocomposites in photonics, biophysics, medicine, and analytical chemistry.