Power Line Communication (PLC) systems provide a bi-directional communication platform capable of delivering data for a variety of Smart Grid applications such as home energy management and intelligent meter reading and control. One benefit of applying power line communication on power grid is that it provides an infrastructure that is much more comprehensive and widespread than other wired/wireless alternatives. Power line cables are a shared medium, therefore multiple PLC devices operate on the same frequency over the same power line may interfere with each other, thus reducing the effectiveness of these devices. This publication introduces the coexistence mechanism for the IEEE and ITU-T BB-PLC standards, and provides implementation guidelines for PLC devices to be used for smart grid applications.