In approximately half of the recurrent spontaneous abortion (RSA) cases, the underlying cause is unknown. However, most unexplained miscarriages are thought to be linked to immune dysfunction. This review summarizes the current evidence regarding the immunological evaluations of patients with RSA, with potential implications for clinical research. The immune system plays a crucial role in the successful outcome of pregnancy, as it tolerates the semi-allogeneic fetus while offering protection to both the mother and fetus from pathogens. The maternal-fetal interface is the place where the crosstalk between various immune cells such as macrophages, dendritic cells, natural killer (NK) cells, and T cells takes place. An adequate balance is required between these immune cells for pregnancy to progress. In RSA, a dysregulation between these immune players is witnessed. For example, in RSA, NK cells are not increased but also undergo a change in their activity, manifested as cytotoxic decidual NK. Similarly, regulatory T cells, which are crucial for fostering a tolerant immune environment, are decreased in RSA women. Similarly, imbalances between T-helper (Th1, Th2, Th17) cell subsets have been implicated in RSA. Furthermore, the imbalance between pro-inflammatory M1 and anti-inflammatory M2 macrophage phenotypes has been documented, with studies indicating a predominance of M1 macrophages in RSA patients. Targeting immune imbalances with therapies such as immunoglobulin administration, TNF inhibitors, and anticoagulants may improve pregnancy outcomes in women with RSA.