Selenium (Se) is a multifaceted element that plays a crucial role in both plant and animal nutrition, yet also poses significant environmental and health risks when present in excess. Selenium’s dual role as both a nutrient and a toxicant necessitates a comprehensive understanding of its agro-environmental dynamics. Selenium is fundamental for plant development and advancement, and its inadequacy can prompt diminished crop yields and debilitated healthful quality. However, excessive selenium levels can be toxic to plants, animals, and microorganisms, causing a range of adverse effects. The threshold between selenium deficiency and toxicity is narrow, and managing selenium levels in agro-environmental systems is a complex challenge. Selenium’s fate and transport in the environment are influenced by various factors, including soil type, pH, and microbial activity. Human activities such as agricultural practices, mining, and industrial processes can lead to selenium contamination of soil, water, and air. The resulting environmental impacts can be severe, including toxicity to aquatic life, soil degradation, and human health risks. Effective management of selenium in agro-environmental systems requires a holistic approach that balances nutritional benefits with environmental and health risks. This involves developing and implementing sustainable agricultural practices, monitoring selenium levels in soil and water, and mitigating contamination through remediation technologies. This part gives an all encompassing comprehension of selenium’s complicated job in agro-ecological frameworks, filling in as an important asset for specialists, policymakers, and professionals trying to adjust the dietary advantages of selenium with its potential natural and wellbeing gambles.