Complex cognitive functions such as learning require coordinated activity across many neurons. Our work uses multisite neurophysiological recordings from behaving animals to investigate how coordinated populations of neurons carry out memory operations, particularly in the hippocampus and entorhinal cortex. The main goals of our work are to understand the functional significance of different types of neuronal coordination patterns within the entorhinal-hippocampal network and to uncover basic cellular and network mechanisms of learning and memory. Understanding the relationship between coordinated neuronal activity and behavior, and determining how coordinated populations of neurons code experiences, is expected to provide novel insights into brain disorders.