The hippocampus is essential for different forms of declarative memory, including social memory, the ability to recognize and remember a conspecific. Although recent studies identify the importance of the dorsal CA2 region of the hippocampus in social memory storage, little is known about its sources of social information. Because CA2, like other hippocampal regions, receives its major source of spatial and non-spatial information from the medial and lateral subdivisions of entorhinal cortex (MEC and LEC), respectively, we investigated the importance of these inputs for social memory. Whereas MEC inputs to CA2 are dispensable, the direct inputs to CA2 from LEC are both selectively activated during social exploration and required for social memory. This selective behavioral role of LEC is reflected in the stronger excitatory drive it provides to CA2 compared with MEC. Thus, a direct LEC → CA2 circuit is tuned to convey social information that is critical for social memory. •Lateral entorhinal cortex (LEC) inputs to hippocampal CA2 underlie social memory•Medial entorhinal cortex (MEC) CA2 input is weak and not involved in social memory•Social memory requires the direct but not indirect LEC inputs to CA2•LEC CA2 inputs are selectively activated by social over non-social exploration Although the CA2 hippocampal region is essential for social memory and detection of social novelty, the inputs that provide social information to CA2 are unknown. We found that social memory depends on the direct inputs CA2 receives from the lateral entorhinal cortex. As this input is activated similarly by novel and familiar individuals, CA2 itself may compute novelty.