Selenium (Se) is a crucial micronutrient with significant implications for plant metabolism, human nutrition, and environmental sustainability. While not essential for most plants, Se interacts closely with sulfur metabolism and influences stress responses, antioxidant defense, and crop resilience. This chapter provides an in-depth exploration of selenium metabolism in crops, detailing its uptake mechanisms, translocation, assimilation pathways, and biochemical transformations. It highlights the molecular and physiological aspects of selenium absorption via sulfate and phosphate transporters, its role in plant stress tolerance, and its biotransformation into organic compounds such as selenocysteine and selenomethionine. The chapter further discusses the environmental factors affecting selenium bioavailability in soils, including pH, redox potential, and microbial interactions. Additionally, it evaluates the implications of selenium biofortification strategies for improving human and animal nutrition, addressing selenium deficiencies, and mitigating toxicity risks. Advances in genetic engineering, nanotechnology, and microbiome-assisted approaches for optimizing selenium uptake and utilization are also explored. A comprehensive understanding of selenium metabolism in crops is vital for developing sustainable agricultural practices that enhance crop productivity while ensuring ecological and nutritional benefits.