The basic functional organization of the cat primary auditory cortex is discussed as it is revealed by electrophysiological studies of the distribution of elementary receptive field (RF) parameters. RFs of cortical neurons have been shown to vary considerably from neuron to neuron; additionally, specific RF properties vary independently. Furthermore, some of the RF properties are nonhomogeneously distributed across the auditory cortex and can be interpreted as forming "maps" that represent specific stimulus information in a topographic way. Accordingly, the functional organization of the primary auditory cortex is interpreted as a series of superimposed independent parameter maps. The consequences of such a layout for the spatial and temporal coding of pure tones and speech sounds is illustrated and ramifications for the interpretation of far-field event-related potentials are discussed.