The present article describes some important effects that the crystalline electric field (CEF) produces in solids and particularly in metals. Emphasis is laid on a description in simple physical terms rather than on detailed mathematical analysis. We first give an outline of the way the CEF acts as a perturbation on the spectroscopic state of the free ion and we discuss briefly the limits of the model including its relation to chemical binding. We then describe the consequences of the CEF interaction including the information that may be obtained from experiment. We discuss the following topics: magnetic moment, susceptibility, magnetic anisotropy, Schottky specific heat, electron paramagnetic resonance, hypertine structure, magnetic form factor, neutron scattering from CEF levels, magnetic excitons and light scattering. In particular we emphasize the relation between CEF effects and neutron scattering because the availability of strong thermal neutron sources will certainly stimulate this field of research.