Silicon is the second most abundant element and accounts for 27–28% of the earth’s crust. Biological systems also contain significant amounts of silicon, as amorphous silica (SiO₂·nH₂O), and its soluble form, silicic acid (Si(OH)₄). Plant dry biomass contains 0.1–10% of silicon. Despite its extensive distribution in plants, silicon is viewed as a quasi-essential element, as most of the plant species can live their entire life in its absence. Interestingly, even in higher amounts, silicon is harmless, noncorrosive, and nonpolluting to plants. It is typically accumulated in the epidermal cells, creating external dual layers of silica-cuticle and silica-cellulose on leaves, stem, and hulls. It thus acts as a physical barrier in plants. Si also alleviates the stress-induced responses in plants. This chapter reviews how plants benefit from silicon under adverse environmental conditions.