This chapter provides fundamental and practical information on the use of ion chambers as detectors in X-ray absorption spectroscopy. Section 1 elucidates the function and limitations of ion-chamber detectors. In Section 2, the phenomenon of recombination in free-air ion chambers is explained using analytical expressions. Using these expressions, the necessary magnitude of applied voltages for current saturation can be obtained. In Section 3, the measurement systems used for current amplification and digitization are described. Noise signal reduction methods are also explained. Section 4 discusses signal contamination due to fluorescence and elastic scattering of the sample, as well as methods to mitigate these effects.