As penetration of photovoltaic (PV) and wind generation systems driven by grid-connected power converters monotonously increases, unusual interactions between innovative and legacy generation systems become more concerning, since they threaten the system stability and reliability. These undesirable interactions are mainly due to the fact that power converters and conventional electromechanical generators currently work under different physical and control principles and rules. This gives rise to some incompatibilities in terms of dynamic response and physical limits, which has become evident once the share of power converters connected to the grid has become relevant enough. In order to address this issue, this chapter presents some relevant concepts for implementing grid-following and grid-forming power converters. In this way, after reviewing some basis on PV and wind generation, this chapter discusses about the operation principle of such power converters, reviewing some fundamentals on grid synchronization strategies and current controllers. After that, some control schemes for gird-forming converters will be presented, paying particular attention to the role of droop control loops and the virtual impedance control. Finally, a general introduction of the synchronous power controller is provided as a preferred implementation of a grid-forming converter based on the virtual synchronous machine concept.