What is the nature of conceptual representations? Models of semantic memory often describe concepts as a distributed feature space. However, it remains unknown which subset of this feature space constitutes the invariant representation of a concept. In this dissertation, I investigate the nature of modality-independent representations and their relationship with words in the mental lexicon. Leveraging the high temporal resolution of magnetoencephalography, I break down the temporal evolution of conceptual and lexical representations within and across two stimulus modalities: pictures and written words. Taken together, my findings outline the temporal dynamics of conceptual and lexical representations, and suggest that modality-independent representations of concrete concepts contain both semantic and visual representations. In contrast, lexical representations did not seem to contribute to the modality-independent conceptual feature space. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]