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.