This chapter describes the plasmonic phenomena. Here, the main models for calculations of complex permittivity of conductors such as Drude, Drude–Sommerfeld, Drude–Lorentz Debye, Brendel–Borman are presented. The author also deals with Helmholtz’s equations for surface plasmon polariton (SPP) waves, their solutions and dispersion equations on the flat and cylindrical interface insulator (or semiconductor)–conductor. This chapter lists calculations of dispersion characteristics made by using formulae of the textbook. The dispersion characteristics of EM waves propagating along the flat gold/silver–air, gold/silver–semiconductor interfaces and also dispersion characteristics of TE0n and TE0n modes for gold cylinders with different radii are thus calculated, and then, the author compares the calculations with analogical results from literature finding that they also coincide.