Certain sensory stimuli -- words, pictures, faces, environmental sounds -- seem to immediately and effortlessly bring to mind a rich array of knowledge that people experience as the "meaning" of those cues. Our research explores the neurobiological basis of meaning processing, asking how world knowledge derived from multiple modalities comes to be organized in the brain and how such information is integrated and made available for use in varied contexts and often in only hundreds of milliseconds. We use human electrophysiological techniques in combination with behavioral, eye movement, and hemodynamic measures to examine how semantic information is structured as a function of modality and stimulus type, how it is brought to bear during language comprehension, and how it is differentially accessed and used by the two hemispheres of the brain. We also examine how these representations and processes change over the course of normal aging.