In electric power systems, phasor measurement units (PMUs) are capable of providing synchronized voltage and current phasor measurements which are superior to conventional measurements collected by the supervisory control and data acquisition (SCADA) system in terms of resolution and accuracy. These measurements are known as synchrophasor measurements. Considerable research work has been done on the applications of PMU measurements based on the as-sumption that a high level of accuracy is obtained in the field. The study in this dissertation is conducted to address the basic issue concerning the accuracy of actual PMU measurements in the field. Synchronization is one of the important features of PMU measurements. However, the study presented in this dissertation reveals that the problem of faulty synchronization between measurements with the same time stamps from different PMUs exists. A Kalman filter model is proposed to analyze and calculate the time skew error caused by faulty synchronization. In order to achieve a high level of accuracy of PMU measurements, innovative methods are proposed to detect and identify system state changes or bad data which are reflected by changes in the measurements. This procedure is applied as a key step in adaptive Kalman filtering of PMU measurements to overcome the insensitivity of a conventional Kalman filter. Calibration of PMU measurements is implemented in specific PMU installation scenarios using transmission line (TL) parameters from operation planning data. The voltage and current correction factors calculated from the calibration procedure indicate the possible errors in PMU measurements. Correction factors can be applied in on-line calibration of PMU measurements. A study is conducted to address an important issue when integrating PMU measurements into state estimation. The reporting rate of PMU measurements is much higher than that of the measurements collected by the SCADA. The question of how to buffer PMU measurements is raised. The impact of PMU meas-urement buffer length on state estimation is discussed. A method based on hypothesis testing is proposed to determine the optimal buffer length of PMU measurements considering the two conflicting features of PMU measurements, i. e. uncertainty and variability. Results are presented for actual PMU synchrophasor measurements.