Magnesium (Mg) is a lightweight metallic element with atomic number 12. It is a very abundant metal, making up roughly 14% of the Earth's mass. It belongs to a group of elements called alkaline earth metals.

The most common magnesium isotope is ²⁴Mg (12 protons, 12 neutrons) but ²⁵Mg and ²⁶Mg are also fairly abundant.

Magnesium has many uses. Being a lightweight metal it has a long history of being used in aircrafts and cars. Magnesium is also a nutrient which is important for bodily functions such as blood pressure regulation and protein production.