Magnesium is the third most abundant structural metal in the Earth's crust and is found in many rock minerals and in seawater. In the soil, it appears in the ionic form Mg2+, in solution and as an exchangeable cation. After absorption, Mg2+ is transported from the roots to the aerial part through the interior of the plant, giving this process the name of translocation. In plants, magnesium plays a fundamental role for growth and development, participating in a series of important processes for the metabolism of the plant, such as the constitution of the chlorophyll molecule, in addition to acting as an enzymatic activator. Thus, given the importance of the magnesium nutrient, the objective of this review is to present the main aspects of this nutrient in the soil and the functions performed in plants.