Titanomagnetite is an Fe–Ti oxide with variable composition (Fe3–xTixO4, 0 ≤ x ≤ 1) and solid solution between magnetite (Fe3O4, x = 0) and ulvöspinel (Fe2TiO4, x = 1) end members. It dominates the magnetism of oceanic basalts, which cover 65% of Earth’s surface. Titanomagnetite is an inverse spinel with variable magnetic properties across its compositional range. Saturation magnetization, anisotropy constant, and Curie temperature values are known for the titanomagnetites, although Curie temperature malleability can make this parameter an inaccurate proxy for composition in natural titanomagnetites. The exchange constant is best known for x = 0 and 0.6. Magnetostriction increases with increasing Ti content due to stresses associated with lattice distortions. The Verwey transition is not observed for low Ti contents, although isotropic points are present over the x < 0.5 compositional range. Magnetic susceptibility is a complex parameter for titanomagnetites because it varies with composition, particle size, and applied field magnitude. While the fundamental magnetic parameters and magnetic properties of titanomagnetite are well understood, knowledge gaps remain that need filling.