This book summarizes the results of studies of molecules and molecular complexes using techniques based on surface plasmon resonance (SPR) in a novel scientific direction called molecular plasmonics. It presents the current state of investigations in the field of molecular plasmonics and discusses its two main physical phenomena: surface plasmon–polariton resonance (SPPR) and localized SPR (LSPR). Among the mathematical methods for the calculation of plasmonic systems response, the book emphasizes models based on the transfer-matrix method, Green function formalism, Mie scattering theory, and numerical methods. It considers the possibilities of the SPPR technique for registering conformational changes, surface plasmon–mediated photopolymerization, electrochemical processes, as well as reversible optoelectronic and physicochemical properties during investigation of molecular systems. It describes applications of the LSPR method, including creation of metamaterials, surface-enhanced fluorescence, and bio- and chemosensing using noble metal nanoparticles in colloidal, array, and composite polymeric film formats. It also highlights the development and applications of plasmonic nanochips.