Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that recognize glycolipid antigens presented by the class I-like non-polymorphic histocompatibility complex (MHC) molecule, CD1d. They express both innate and adaptive immune cells’ surface receptors, but act more like cells of the innate immune system. Although iNKT cells represent a relatively small population of T lymphocytes, they can rapidly produce copious amounts of cytokines after activation which can polarize different axes of the immune response. Many glycolipid agonists have been discovered of which the marine sponge-derivative called α-Galactosylceramide (α-GalCer) is a potent ligand for iNKT cells. iNKT cells have been described by many researchers as a critical immunotherapeutic target characterized by having tumor-suppressive potential. However, their actual role in immune responses is still unclear. In addition, the need for appropriate preclinical models that mimic human diseases is important for better understanding the iNKT cell biology. This review describes the characteristics of iNKT cells and their role in immunotherapy in cancers such as multiple myeloma and how they can interact with the components of the neighbouring environment.