Selenium (Se) is a vital micronutrient that is important for the well-being of human and animals alike. Plants are the primary contributors of Se within the food chain. Metals that possess a density exceeding 5 g cm−3 are categorized as heavy metals. These metals are non-degradable and remain in the soil for a long time, which is where the danger lies. Heavy metal pollution is one of the most serious abiotic problems facing the world. Heavy metals such as Cd, Pb, Hg, and As are produced from two main types of sources: natural sources, as these metals are found naturally in the earth's crust, and anthropogenic sources such as various industrial activities, excessive use of fertilizers and pesticides, or the use of untreated wastewater for irrigation of plants, and many other sources. Heavy metal pollution of the environment is a serious problem since it not only reduces crop output but also poses health concerns to humans and animals when feeding on contaminated plants. Applying selenium is one of the chemical remediation techniques that lessens the detrimental effects of pollutants on plant growth and development, which lowers crop productivity. This, in turn, limits the contaminants’ access to the human body and the health concerns they pose. Selenium is essential for the development of plants’ defense mechanisms because it keeps some heavy metals from being absorbed and transported within the plant, enhances the antioxidant system, and helps the cell produce a lot of osmolytes, which keeps the water balance stable. Additionally, selenium generates a number of secondary metabolites that aid in plants’ defense against heavy metal stress. Thus, in addition to discussing the forms of selenium that plants prefer for absorption and the conditions that facilitate its absorption from the soil and water, this book chapter delves deeply into the role of selenium in enhancing the mechanisms of resistance of plants to the adverse effects resulting from the absorption of toxic heavy metals.