Network oscillations are proposed to provide the framework for the ongoing neural computations of the brain. Thus, an important aspect of understanding the functional roles of various cell classes in the brain is to understand the relationship of cellular activity to the ongoing oscillations. While many studies have characterized the firing properties of cells in the hippocampal network including granule cells, pyramidal cells and interneurons, information about the activity of dentate mossy cells in the intact brain is scant. Here we review the currently available information and describe biophysical properties and network-related firing patterns of mossy cells in vivo. These new observations will assist in the extracellular identification of this unique cell type and help elucidate their functional role in behaving animals.