A basic role of the auditory system in all mammals is to identify sounds and use this information to selectively activate neural systems that focus attention on the sound, or generate a suitable motor response. In the first relay center, i.e. the cochlear nuclear complex, the signals of the cochlear nerve diverge into a number of parallel ascending tracts that converge on the auditory midbrain, the inferior colliculus. In contrast to the role of the superior colliculus within the visual system, the IC is the principal source of input to the auditory thalamus (Malmierca, 2003). Likewise, there is a minimum of three relays in the auditory system, with several stages of convergence and divergence, and at least seven levels of crossing as opposed to the minimum of two relay stations between the periphery and cerebral cortex in the other sensory systems. The auditory system is unique among sensory systems because it integrates a highly complex network of pathways in the lower brainstem, with a significant amount of processing accomplished in the IC, just prior to the level of the thalamus. The IC probably represents a major output to premotor pathways that initiate or regulate sound-evoked motor behaviour (Casseday et al. 2002). Of all the brainstem and midbrain auditory structures, the IC has been studied comprehensively by many investigators possibly because it is more easily accessible and highly differentiated than many other parts of the auditory brainstem in both speciealized and non-speciealized mammals (for detailed reviews see e.g. Malmierca, 2003; Winer & Schreiner, 2005). The IC is not only the main site of termination for the ascending fibers of the lateral lemniscus but also eceives a heavy innervation from the auditory cortex Furthermore, the IC receives crossed projections from its contralateral counterpart (Malmierca et al. 1995) and possesses a dense network of local connections (Malmierca et al. 1995). Thus, the IC occupies a strategic position in the central auditory system and may be considered as a central hub or an interface between the lower auditory pathway, the auditory cortex and motor systems (Casseday et al. 2002). In this paper, I shall review recent anatomical and physiological experiments which demonstrate that the inferior colliculus is involved in a great diversity of functional roles in the auditory system, and that most of the interesting auditory features might already be extracted from incoming sounds by this midbrain nucleus. Therefore, the inferior colliculus may even be considered as the auditory analog of the primary visual cortex, so that as suggested by Nelken (2004), the role of the auditory cortex might be to organize these features into auditory objects.