Magnesium is an important cofactor in biological processes. For many years it has been considered that magnesium homeostasis in a cell is regulated by its eflux from a cell and not by its influx. It has also been considered that the Na+/Mg2+ antiport plays the main role. In recent years, many experiments have been carried out to understand the mechanisms of Mg2+ transport in an organism. These experiments have led to some new conclusions. It was confirmed that the level of magnesium in a cell is probably also regulated by its influx to the cell. One of the last scientific findings is the discovery of the TRPM (transient receptor potential melastatin) protein family. TRPM6 and TRPM7, bifunctional proteins with kinase and ion channel activities, are responsible for magnesium homeostasis. The discovery of these proteins led to a better understanding of magnesium homeostasis. It was confirmed that TRPM6 protein is responsible for homeostasis in the whole organism and that TRPM7 may regulate the level of magnesium in the cell. TRPM7 also has other functions. One of those newly recognized is the phosphorylation of annexin 1. However, many activities and functions of TRPM7 have not yet been described. This paper is a review of knowledge of TRPM7 transmembrane protein, which is responsible for the magnesium homeostasis in the cell. It briefly presents the main functions and structure of TRPM7. It also describes the mechanisms of its biological activity.