Moving toward green energy technologies will introduce more technical challenges to the modern interconnected energy systems with power systems. To address these challenges, it is necessary to understand the basics of power systems and the new technologies integrated to the power systems. Among the emerging technologies, power electronics play a significant role in various applications. Depending on how to design, control and operate the power electronics, they can strengthen or deteriorate the performance of the whole system. This monograph provides an overview of the modern electric energy systems with more power electronics integration in generation, operation and control perspectives. The basics of power systems are introduced and the fundamentals of transition from traditional centralized power systems to modern power systems are discussed. Thereafter, dominant clean energy generations are introduced, and the basics of power converter topologies and control structure are explained. Lastly, the concept of reliability assessment in power electronics-dominated power systems is covered. Also, major technical challenges that are deteriorating the overall system performance and reliability are addressed and feasible solutions are explained.