A survey is given of the origins of constant modulus behavior in certain ferro- and antiferromagnetic alloys. All contributions to the modulus anomaly ( ∆Ε) result from magnetic ordering. In the Fe-Ni system various influences are studied in detail; Ternary alloying elements, precipitation hardening process, cold reduction and final thermal treatment. The thermoelastic properties of a technical constant modulus alloy were investigated in magnetic dc fields up to 300 A/cm for various vibrational modes; the influence of the skin-effect was detected for f > 30 kHz. Some dynamic applications (e.g. electromechanical filters, frequency standards, delay lines) are described.