A treatment of the Fermi-liquid theory of high-frequency phenomena in metals, in paricular the effects due to local features in the geometry of the Fermi surface. The text develops a consistent theory of several effects, such as cyclotron resonances in magnetic fields normal to the surface. Topics covered include: basic equations of the Fermi-liquid theory; cyclotron Doppler on waves; local anomalies in the Fermi surface; cyclotron resonancce in metals; magneto-acoustic oscillations and the local geometry of the Fermi surface.