Selenium, an essential trace element, exhibits a complex global and regional distribution pattern that significantly impacts human health. This chapter explores the selenium footprint, highlighting its geographical variability and the implications of both deficiency and excess. Selenium levels in the environment are influenced by geological factors, leading to marked differences in soil and dietary selenium concentrations across regions. Selenium-rich soils have been linked to higher dietary intake and lower incidences of Keshan disease associated with selenium deficiency. Conversely, regions with low selenium availability often experience health complications, including growth retardation and increased inflammation. Environmental factors such as climate and soil type significantly affect selenium's bioavailability and mobility. Wet and dry deposition processes can introduce selenium into ecosystems, while changes in groundwater levels can lead to fluctuations in selenium concentrations in aquatic systems. Additionally, microbial activity influences the biogeochemical cycling of selenium, which can alter its oxidation states and speciation, further impacting its environmental distribution. Understanding the global and regional distribution patterns of selenium is vital for addressing public health concerns related to its deficiency and toxicity. As climate change progresses, predictions indicate that selenium deficiency risks may increase, particularly in vulnerable regions. Therefore, comprehensive monitoring and management strategies are essential to ensure adequate selenium levels in the environment for human health and ecological balance.