This paper describes a novel fault-detection technique of high-impedance faults (HIFs) in high-voltage transmission lines using the wavelet transform. The wavelet transform (WT) has been successfully applied in many fields. The technique is based on using the absolute sum value of coefficients in multiresolution signal decomposition (MSD) based on the discrete wavelet transform (DWT). A fault indicator and fault criteria are then used to detect the HIF in the transmission line. In order to discriminate between HIF and nonfault transient phenomena, such as capacitor and line switching and arc furnace loads, the concept of duration time (i.e., the transient time period), is presented. On the basis of extensive investigations, optimal mother wavelets for the detection of HIF are chosen. It is shown that the technique developed is robust to fault type, fault inception angle, fault resistance, and fault location. The paper demonstrates a new concept and methodology in HIF in transmission lines. The performance of the proposed technique is tested under a variety of fault conditions on a typical 154-kV Korean transmission-line system.