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Synchronized phasor measurements (PMU) were introduced in mid-1980s. Since then, the subject of wide-area measurements in power systems using PMUs and other measuring instruments has been receiving considerable attention from researchers in the field. This paper provides a historical overview of the PMU development. It is pointed out that the PMU is a direct descendant of the symmetrical component distance relay introduced in the late 1970s. From the early prototypes of the PMU built at Virginia Tech, a commercial product evolved which has been installed in the field at various locations around the world. Applications of PMU measurements to power system operation and control remains a very important subject for current research.