Ferritin is a highly conserved, ubiquitous intracellular iron storage protein that plays a crucial role in iron homeostasis by safely and reversibly storing iron, thus preventing its toxicity and providing a readily available source for the synthesis of heme and iron-containing proteins. It is composed of 24 subunits, typically of two types in humans: the heavy (H) and light (L) subunits, which assemble into a hollow, spherical protein nanocage structure. The proportion of H and L subunits varies among different tissues, with H-rich ferritins found in organs like the heart and brain, and L-rich ferritins in the liver and spleen. Ferritin's iron storage capacity is remarkable, as it can accumulate up to 4,500 iron atoms within its protein shell. Additionally, ferritin has antioxidant properties by sequestering free iron and consuming reactive oxygen species. In clinical medicine, ferritin is predominantly utilized as a serum marker of total body iron stores. In cases of iron deficiency and overload, serum ferritin serves a critical role in both diagnosis and management. Elevated serum and tissue ferritin are linked to coronary artery disease, malignancy, and poor outcomes following stem cell transplantation. Ferritin is directly implicated in less common but potentially devastating human diseases including sideroblastic anemias, neurodegenerative disorders, and hemophagocytic syndrome.