The magnetic susceptibility of n-type silicon samples with a wide range of donor concentrations (3×1016 to 3×1019 atoms/cm3) has been measured as a function of temperature from 3°K to 300°K. By utilizing conduction-electron concentrations obtained from Hall coefficient measurements on comparison specimens over the range from 50°K to 400°K, the contributions to the susceptibility arising from the conduction electrons and electrons trapped on donor atoms have been analyzed. In the upper range of temperature the diamagnetic contribution of conduction electrons is dominant and is consistent with the model of six energy minima in the conduction band. However, comparison of the squared reciprocal mass ratio with that obtained from cyclotron-resonance experiments reveals that the former is appreciably smaller than the latter (~8 as compared to ~13). As the temperature is lowered, the conduction-electron contribution becomes successively less as electrons are frozen out on donor atoms. The trapping of electrons by donors at low temperatures leads to a Curie-law paramagnetism in the specimens of higher purity, whereas in the more impure samples, deviations from Curie's law occur which are attributed to interactions between closely spaced donor centers.