This chapter theoretically demonstrates that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media due to the possibility of stimulated electron tunneling accompanied by emission of plasmons under application of interlayer voltage. The plasmon dispersion develops an anticrossing with the resonances in tunnel conductivity and demonstrates negative group velocity in several frequency ranges. The chapter shows that the dynamic and nonlocal effects in the tunnel conductivity radically change the picture of plasmon propagation. It derives the dispersion relation for plasmons in tunnel-coupled graphene layers. The chapter devotes to the calculation of high-frequency nonlocal conductivity, which possesses both tunneling and in-plane components. It also devotes to the effect of interlayer twist on high-frequency conductivity and SP dispersion. Possible experimental manifestations of the predicted effects are discussed. The evaluation of interlayer conductivity is based on the solution of the quantum Liouville equation for the electron density matrix.