The inertia welding process as developed by research engineers at Caterpillar Tractor Co. has found many applications in the manufacture of earthmoving machinery. This metals-joining process derives power from energy stored in a rotating flywheel system. When two components to be joined are brought into contact by thrust pressure, the energy is converted to heat through friction at the interface, permitting formation of a solid-state bond. Initially applied to replace other metals-joining methods, to solve specific problems, or to effect cost savings, inertia welding is now a basic consideration in new product design. The evolution of the inertia welding process and inertia welders from the laboratory to today, in relation to earthmoving machinery applications, is discussed in this paper.