The purpose of the present thesis was threefold. First, to study perceptual and cognitive correlates to individual differences in speechreading performance. Second, to examine certain aspects of word-decoding/discrimination in the speechreading process. Third, to investigate whether hearing-impaired individuals compensate for their hearing loss by means of improved speechreading ability. The results demonstrate that individual differences on a set of perceptual and cognitive component processes were related to speechreading either directly or indirectly, and could also be classified as influencing speechreading generally or specifically. Based on this 2 by 2 taxonomy, it was thus possible to establish which kind of relationship and what kind of effect a certain cognitive component is responsible for in speechreading. The results also indicate that there are similarities between visual and auditory speech perception in the temporal order that words are recognized. A process model for speechreading was also developed and further test implications were delineated. The results do not indicate that hearing-impaired individuals compensate for their hearing loss by means of an improved speechreading ability, neither do they rely on a different set of cognitive components for successful speechreading.