Permalloy (Fe-Ni system alloy) and Permendur (Fe-Co system alloy) have excellent soft magnetic characteristics. Many types of alloys with various chemical compositions have been developed since both were invented about 100 years ago. Two typical compositions of the Permalloy are Fe-45 mass% Ni and Fe-78 mass%, while the Permendur has generally a typical composition of Fe-49 mass% Co-2 mass% V. Major applications of the Permalloy are sensors and magnetic shielding because of its superior magnetic permeability to other soft magnetic materials. On the other hand, the Permendur is used in generator cores for aircraft or motor cores for racing cars because of its high magnetic flux density and low core loss characteristics. These excellent soft magnetic properties of both alloys cannot be obtained with the other soft magnetic materials. Accordingly, these two alloys will be widely used especially in high-tech areas in future, although both alloys are relatively expensive due to their high-alloy systems. This chapter describes production process, structural/magnetic properties, and application examples of these two distinctive types of soft magnetic alloys including their development histories.