Though distributed generators (DGs) have significant economic and environmental benefits, increased penetration of DGs will impose significant technical barriers for the efficient and effective operation of bulk power systems. Increased fault current contribution and load flow changes are the major two impacts on utility systems, and these will affect existing protective relaying, especially overcurrent relays. To ensure safe and selective protection relay coordination, the impact of DGs should be taken into account when planning DG interconnection. This paper presents an introduction of DGs and an overview of the impacts of DGs on system protection relay coordination. Several protection issues are identified to study the requirements for protection in the presence of DGs are also discussed.