In the course of everyday tasks, we must often remember information across brief delays. Behavioral studies suggest that we can remember up to 3 to 4 items simultaneously. Beyond this limit, performance drops substantially. However, little is known regarding how the brain represents multiple items in working memory. This dissertation examines through electrophysiological recordings from behaving monkeys during a change localization task, in which animals viewed two displays of colored squares separated by a brief delay, and made an eye movement to the square that changed between the two displays. In chapter 2, we examine local field potentials recorded from the lateral intraparietal area (LIP), frontal eye field, and lateral prefrontal cortex (PFC). At stimulus encoding, lower frequency oscillations decreased in power in proportion to the total number of stimuli to be encoded, while higher frequency oscillations increased in power in proportion to the number of stimuli contralateral to the recording site. During the delay, lower frequency power instead increased with the number of contralateral stimuli, while higher frequency power was not modulated. We interpret these findings in terms of roles for low- and high-frequency oscillations in top-down and bottom-up stimulus processing. In chapter 3, we compare spiking activity between LIP, PFC, and inferotemporal cortex (IT). Although the task required that the animal remember stimulus colors, activity in LIP and PFC primarily reflected the stimulus positions and only weakly reflected color. Activity in IT primarily reflected color, but also weakly reflected position. In PFC, variance in firing rate explained by stimulus colors increased with the number of stimuli presented, while in IT, explained variance remained constant or decreased. Thus, IT was more strongly capacity-limited than PFC. Color selectivity during the delay was weak in all regions. However, in IT, activity at test stimulus presentation reflected the difference in square colors between the sample and test displays, while in PFC, activity primarily reflected the location of the changed square. Selectivity to these attributes was stronger on correct trials than incorrect trials. Our findings suggest a possible role for passive memory processes in IT in working memory performance.