Graphene plasmonics, which studies the collective oscilla tion of massless Dirac fermions inside graphene, merges two vibrant fields of study: Graphene physics and plasmonics. The propagation of surface plasmon polaritons (SPP) waves in the one-atom-thick graphene can be largely controlled by graphene's tunable surface conductivity via chemical dop ing or electrostatic gating. Graphene is a well-known mate rial whose plasma frequency can range broadly from direct current (DC) to infrared, sensibly depending on the carrier density or Fermi level. The intriguing plasmonic properties of graphene open tremendous new possibilities in tunable and switchable novel terahertz (THz) and infrared optoelectronic devices, with features of compact size, ultrahigh speed, and low power consumption. In this chapter, we will review the theory and recent findings on graphene plasmonics. We pres ent current advances and future applications of graphene plas monics in the extreme manipulation of light at the nanoscale.