Power conversion efficiency of single-junction solar cells is fundamentally limited by the Shockley- Queisser (S-Q) limit. The most promising practical technology to break through the S-Q limit is to use two-terminal tandem structure which can simultaneously solve the problems, spectral mismatch and thermal relaxation energy loss, in single-junction devices. As one of the important components of the interconnecting layer, the recombination layer in the two-terminal tandem solar cells can provide recombination sites for electrons and holes extracted from the electron transporting layer and the hole transporting layer, avoiding the open-circuit voltage loss caused by charge accumulation and promoting the current flow of tandem solar cells. The recombination layer is considered as one of the key factors of achieving high-performance tandem devices. The ideal recombination layer should possess high conductivity to improve the charge recombination rate, high optical transmittance to ensure effective light absorption of the rear subcells, good chemical stability to reduce the damage caused by the solvent, and low preparation cost to promote the commercial production process. At present, a variety of materials have been used in two-terminal tandem solar cells, such as thin metals, transparent conductive oxides, conductive polymers, graphene oxide, etc., which play an important role in perovskite-perovskite, perovskite-organic, and perovskite-silicon two terminal tandem devices. In this review, the research progress of recombination layers in different types of tandem solar cells is summarized, together with types, design principles, preparation processes, and their advantages and disadvantages. Meanwhile, problems and challenges of the current recombination layers are proposed, which provides a useful reference for the design of high-performance tandem cells.