The complexity of cancer biology exceeds the uncontrolled proliferation of neonatal cells to include the crosstalk between tumors and their microenvironments (TME). Specifically, the histamine-producing cells constitute a key component of TME given their “immunoediting” role that would ultimately determine the disease outcome. Histamine is not only one of the potent mediators that intensify/perpetuate the inflammatory responses; it also exerts a plethora of fine-tuned immunoregulatory effects through coupling with G-protein coupled receptors (HRs) ubiquitously distributed on almost all mammalian cells. In the context of cancer biology, histamine plays a multifaceted role in tumor progression, where it acts as a pro- or anti-tumorigenic mediator depending on the cancer type and the cognate receptor. This chapter addresses the immunomodulatory role of histamine and its cognate receptors in tumor immunobiology, in addition to compiling cutting-edge approaches to their potential use as adjuvants in cancer immunotherapy.