Bimolecular Fluorescence Complementation (BiFC) is a biological imaging technology used to study protein interactions. By connecting two parts of the target protein to two complementary fragments of a fluorescent protein, when the two parts bind to each other, the fluorescent protein reassembles, producing a fluorescent signal. BiFC can monitor the spatiotemporal dynamics of protein interactions in living cells in real time, providing an intuitive, high-resolution tool for cell signaling and protein interaction research.