[en] The weakly relativistic description of wave propagation and absorption in the electron cyclotron range of frequencies is reviewed. After a brief discussion of the relativistic cyclotron resonance condition, we derive the weakly relativistic dielectric tensor of a Maxwellian plasma in the form which is now canonical, in terms of the relativistic Plasma Dispersion functions of Dnestrovsky and Skarofsky. The most useful analytic properties of these functions are summarized. We then obtain the small Larmor radius approximation, which is sufficient for most practical purposes when investigating electron cyclotron heating and current drive in tokamak plasmas. Finally, we present some solution of the finite Larmor radius dispersion relation near the fundamental and its first harmonic, respectively, emphasizing in particular the shape of the cyclotron absorption lines and the differences between the relativistic results and the classical limit. (orig.)