Recent works made by the authors' research group on magnetic field-induced martensitic transformations are reviewed, which are concerned with some ferrous alloys and steels. Main results of the works are as follows: The effect of magnetic fields on martensitic transformation start temperature is quantitatively explained by cumulative three energies, that is, magnetostatic energy, high field susceptibility energy and forced volume magnetostriction energy. Antiferromagnetic order in the parent phase suppresses the martensitic transformation. The appearance of magnetoelastic martensitic transformation is newly found in an ausaged Fe-Ni-Co-Ti alloy. Futhermore, directional growth of magnetic field-induced martensite plates is observed parallel to the magnetic field.