Brain temperature is a physiological parameter, reflecting the balance between metabolism-related intra-brain heat production and heat loss by cerebral circulation to the rest of the body and then to the external environment. First, we present data on brain temperature fluctuations occurring under physiological and behavioral conditions and discuss their mechanisms. Since most processes governing neural activity are temperature-dependent, we consider how naturally occurring temperature fluctuations could affect neural activity and neural functions. We also consider psychomotor stimulants and show that their hyperthermic effects are state-dependent and modulated by environmental conditions. Since high temperature could irreversibly damage neural cells and worsen various pathological processes, we consider the situations associated with pathological brain hyperthermia and evaluate its role in acute perturbations of brain functions, neurotoxicity, and neurodegeneration. We also discuss the limitations in consideration of brain temperature within the frameworks of physiological regulation and homeostasis. While different adaptive mechanisms could, within some limits, compensate for altered intra-brain heat balance, these mechanisms could fail in real-life situations, resulting in life-threatening health complications.