Two classes of magnetostrictive materials are emerging which can strongly impact magnetomechanical transduction and high-stress antivibration systems. One class utilizes highly magnetostrictive rare earths with anisotropic 4f electron shells. The second class is based upon α−Fe, with substitutions of nonmagnetic Ga and Al for Fe. The first class contains three distinct types of materials: (a) hexagonal Tb1−xDyx alloys, (b) cubic CsCl type Tb1−xDyxZn alloys, and (c) cubic Laves phase Terfenol alloys. While the first two types produce extraordinarily high magnetostrictions only at cryogenic temperatures, Terfenol alloys exhibit large magnetostrictions (>1000 ppm) at 200<th>°C and above. This paper will focus on recent measurements on low-hysteresis Terfenol-DH alloys taken between −40<th>°C–+80<th>°C. The new class of promising high-strength, low-cost, Fe-based alloys will also be introduced. Here the emphasis is on the development of a ductile, high tensile-strength material with high strains (>300 ppm ), high relative permeabilities (>100), and low excitation fields (<300 Oe) under high loads. Magnetostriction, magnetization and elastic constant measurements as a function of stress and magnetic field will be presented. Values of piezomagnetic constants and coupling factors, calculated from these measurements, will be included. [Work supported by ONR.]