The bimolecular fluorescence complementation (BiFC) technique is a powerful tool for visualizing protein-protein interactions in vivo. It involves genetically fused nonfluorescent fragments of green fluorescent protein (GFP) or its variants to the target proteins of interest. When these proteins interact, the GFP fragments come together, resulting in the reconstitution of a functional fluorescent protein complex that can be observed using fluorescence microscopy. In this chapter, we provide a detailed overview of the BiFC method and its application in studying protein-protein interactions in mouse hippocampal neurons. We discuss experimental procedures, including virus construct design, neuronal transduction, and imaging optimization. Additionally, we explore complementary assays for result validation and address potential challenges associated with BiFC experiments in the neuronal system. Overall, the BiFC offers researchers a valuable approach for investigating the spatial and temporal dynamics of protein interactions in living neuronal cells.