The artificial light at night (ALAN) is increasing worldwide due to the development of new lighting technologies, their reduction in cost and their rapid adoption. ALAN and resulting light pollution can cause a significant effect on the endogenous circadian rhythms of physiological, biochemical and behavioral functions in mammals. Intrinsically photosensitive retinal ganglion cells (ipRGC) received the light information and then send it to the central pacemaker of the circadian timing system – suprachiasmatic nucleus, located in the anterior part of the hypothalamus (SCN). The SCN relays timing information to all cells of the body, including the pineal gland, which secrets the hormone melatonin, involved in the regulation of the biological rhythms. Exposure to ALAN inhibits the melatonin synthesis and lead to behavioral disturbances and shifts in the timing of reproduction in wild mammals. Despite active research in this area, the role of the pineal gland and melatonin in the mechanisms of adaptive responses in mammals when exposed to light at night has not been thoroughly studied. This review discusses the need for further comprehensive research of the effects of ALAN in mammals.