Medium voltage (MV) crosslink polyethylene (XLPE) power cables are extensively utilized in power distribution networks throughout the world. Reliable power delivery depends on the condition of the power cable and distribution system network components. Failure of power cables can cause loss in terms of power outages, capital, and human resources. This is a prime area for research. Degradation of the physical properties of the insulation over time is the usual cause of power cable failure. Factors responsible for XLPE cable degradation include but are not limited to mechanical, electrical and chemical stresses, flaws in manufacturing, and conditions in the environment. The aforesaid degradation factors cause water trees, electrical trees and partial discharge, and finally result into power cable failure. The nonlinear nature of a water tree results in harmonic generation in the AC loss current. The magnitude of the higher harmonics thus generated, depends on the amount of nonlinearity, therefore, amplitude and phase angel of the third harmonic current can be utilized to detect and quantify the degradation level. The main objective of this papers is to present a brief review on methods introduced in literature to utilize the third harmonic current as a diagnostic tool to identify and quantify the power cable degradation. © 2012 IEEE.