The integration of distributed generation (DG) units into a distribution system leads to a number of technical, environmental and economic bene?ts. However there are several issues regarding connection of these resources to utility. One of the technical concerns associated with DG units is the islanding phenomenon. Islanding is a condition in which a part of the utility system, which contains load and generation, is isolated from the rest of the utility system and continues to operate. Islanding is either intentional, as for maintenance and load shedding, or unintentional as with faults and equipment failures. Because of disadvantages of islanding such as safety hazard, the standards do not allow islanding (unintentional) and necessitate DG’s disconnection once an islanding condition occurs. Several techniques have been proposed for islanding detection in the literature. In this thesis, performance of several passive islanding detection methods for inverter-based DGs is investigated. The impact of DG interface control on islanding detection and NDZ of OVP/UVP and OFP/UFP methods is examined. The NDZ for over/under voltage and over/under frequency is derived analytically for each interface control and validated by simulation. DGs are normally operated at a unity power factor and in case of islanding, the frequency drifts based on the reactive power mismatch between the load and DG. However, for DGs that supply reactive power to provide unity power factor improvement, the performance of OVP/UVP and OFP/UFP methods might change. It is observed that the NDZ of the OVP/UVP and OFP/UFP is larger when the DG interface is designed to improve the power factor. An islanding detection method is investigated that is based on creating a mismatch between the load and DG reactive power, thus forcing the frequency to deviate outside the OFP/UFP limits. Also, this method is implemented on constant current controlled inverter. The local load’s type is an effective factor on the islanding detection methods. Usually in distributed generation islanding detection studies, constant RLC loads were supposed as the worst detectable case. Since the polynomial load model is more suitable for modeling of distribution system loads, in this thesis, the performance of the OVP/UVP and OFP/UFP methods is tested for this type of the loads. Several loading conditions with different parameters of the load are considered and the results are compared with constant RLC load case. The constant power-controlled and constant current controlled interface control of inverter-based DG is designed to operate at unity power factor. The NDZ is derived analytically in terms of the load’s parameters. One of the passive islanding detection methods is detection of voltage harmonics. Keywords: Inverter-based DG, Islanding detection, Passive detection methods, Static load models, Detection of voltage harmonics