Since power systems are susceptible to damages induced by disastrous incidents, the assessment and improvement of system resilience are unavoidable as a new goal of planning and operation. On the other hand, the expansion of generation and transmission grids constitute an essential part of power system planning as it needs a huge budget. So, a primary concern of researchers has always been the optimal planning of power systems. This paper studies the emerging concept of resilience, its criteria, and indicators, how to enhance it, and the identification of its strengths and weaknesses. It also reviews the strategies recommended in the literature to improve power system resilience. The paper briefly reports the models for expansion plan analysis and the generation and transmission expansion planning (GTEP) tools with or without the target of resilience enhancement, which can be instrumental in future research and can be used to estimate the effectiveness of different tools. Furthermore, the paper discusses the planning problems, thereby opening the way for further work in future studies. Finally, the study presents the most eminent challenges of GTEP to accomplish better, resilient, and innovative plans to escalate power system resilience.