Fever is a conserved response to infection in vertebrates, involving integrated physiological and neuronal circuits that enhance survival during infection. This review discusses how fever-induced inflammatory signals stimulate innate and adaptive immune responses, highlighting the role of the pyrogenic cytokine interleukin-6 (IL-6) in fever induction and lymphocyte trafficking. It also explores how adrenergic signaling pathways involved in thermogenesis influence immune cell function. Fever is closely linked to inflammation, with febrile temperatures improving survival and resolving infections. However, fever is not universally beneficial, especially in severe inflammation, where cooling may be protective. Studies show that fever enhances immune responses by increasing the effectiveness of both innate and adaptive immunity, and that IL-6 plays a key role in this process. Fever also acts as a 'rheostat' to regulate systemic inflammation during recovery. The review highlights the role of IL-6 in fever induction and lymphocyte trafficking, as well as the overlapping signaling pathways between thermogenesis and immune regulation. It also discusses the impact of fever on immune cells, including neutrophils, NK cells, and dendritic cells, and how fever enhances immune responses by promoting lymphocyte trafficking and activation. Fever also enhances the function of T cells and increases the production of pro-inflammatory cytokines. The review concludes that fever is an evolutionarily conserved response that enhances immune function, and that understanding the mechanisms of fever could lead to new therapeutic strategies for cancer immunotherapy.Fever is a conserved response to infection in vertebrates, involving integrated physiological and neuronal circuits that enhance survival during infection. This review discusses how fever-induced inflammatory signals stimulate innate and adaptive immune responses, highlighting the role of the pyrogenic cytokine interleukin-6 (IL-6) in fever induction and lymphocyte trafficking. It also explores how adrenergic signaling pathways involved in thermogenesis influence immune cell function. Fever is closely linked to inflammation, with febrile temperatures improving survival and resolving infections. However, fever is not universally beneficial, especially in severe inflammation, where cooling may be protective. Studies show that fever enhances immune responses by increasing the effectiveness of both innate and adaptive immunity, and that IL-6 plays a key role in this process. Fever also acts as a 'rheostat' to regulate systemic inflammation during recovery. The review highlights the role of IL-6 in fever induction and lymphocyte trafficking, as well as the overlapping signaling pathways between thermogenesis and immune regulation. It also discusses the impact of fever on immune cells, including neutrophils, NK cells, and dendritic cells, and how fever enhances immune responses by promoting lymphocyte trafficking and activation. Fever also enhances the function of T cells and increases the production of pro-inflammatory cytokines. The review concludes that fever is an evolutionarily conserved response that enhances immune function, and that understanding the mechanisms of fever could lead to new therapeutic strategies for cancer immunotherapy.