Human memory has been divided into two major classes of information: episodic memory, which is memory for specific events or episodes of one's life (e.g., what one ate for breakfast this morning); and semantic memory, or factual memory, which is described as memory for knowledge about objects, facts, concepts, and words and their meanings (e.g., what are suitable breakfast foods). Research in my lab focuses on the latter, in our investigations of the neural basis of semantic memory. Relatively little is known about the cortical systems that subserve the storage and retrieval of semantic knowledge, despite numerous cases of dramatic semantic memory dysfunction, such as that observed as one of the earliest and most prominent feature of Alzheimer's disease and other dementing diseases. Recent advances in neuroimaging which provide a noninvasive method for studying normal cognition in healthy volunteers have allowed great strides in understanding the neural bases of cognition. Perhaps nowhere has this method been as influential as in the study of semantic memory. In my laboratory, we take advantage of the latest techniques in functional neuroimaging (fMRI) to answer questions about how and where semantic memory is stored and organized in the brain and how that knowledge can be selectively and flexibly retrieved when needed. Much of our recent research has focused on the role of one region of cortex, the frontal lobes, in the task of retrieving semantic information. In conjunction with our neuroimaging studies, we also examine these questions in brain-damaged humans, in order to provide convergent evidence which is additionally capable of revealing the necessity of brain regions for various cognitive functions. The combination of fMRI studies of normal humans and behavioral studies of patients with relatively focal brain lesions has proven to be an extremely useful approach in our investigations of semantic memory. We have also used both of these methods, in addition to experimental studies of normal humans, to address related topics, such as the role of the frontal lobes in episodic and short-term memory retrieval.