This chapter introduces cognitive science and psycholinguistic assumptions about word processing and the structure of the mental lexicon. After a brief explanation of the neurocognitive processes of object recognition and knowledge representation, findings on the functional neuroanatomy of word processing and the constitution of meaning are presented. The neurolinguistic findings are embedded in psycholinguistic hypotheses on the processing of spoken language and on concepts of meaning such as schema, script and mental concept. The comparatively well-researched concept of a single mental lexicon or different mental lexicons and their cortical representation form a focus of neurolinguistic research.