In this chapter we discuss the propagation of small amplitude waves in a hot magnetized plasma. Just as for a cold plasma, the presence of a static zero-order magnetic field in a hot plasma leads to a wide variety of new phenomena. Because the zero-order motions of the particles in a magnetized plasma consist of circular orbits around the magnetic field, some type of resonance can be expected when the wave frequency is equal to the cyclotron frequency. In a cold plasma, this resonance is the same for all particles of a given charge-to-mass ratio, and gives rise to the well-defined cyclotron resonances described in Chapter 4. In a hot plasma, the frequency “felt” by a particle is Doppler shifted by the thermal motion of the particle along the static magnetic field. For a given parallel velocity, resonance occurs when the frequency in the guiding center frame of reference of the particle is at the cyclotron frequency, i.e., ω′ = ω − k∥ν∥ = ωc. Because of the thermal spread in the particle velocities, the resonance is no longer sharp, as it was in a cold plasma, but is now broadened by the thermal motion. The resonant interaction also produces damping, called cyclotron damping, in a manner somewhat analogous to Landau damping. If the cyclotron radius of the particle is a significant fraction of the wavelength, the phase shift introduced by the periodic cyclotron motion of the particles back and forth along the perpendicular component of the wave vector produces a phase modulation at the cyclotron frequency.