As the penetration level of inverter-based resources (IBRs) in the existing power systems continues to increase, the system faces challenges in maintaining sufficient inertia, inverter modeling and control, coordination among multiple assets and plants, stability analysis, and large-scale interconnection in both distribution and transmission systems, among others. More importantly, grid resiliency could be challenged significantly by the complex dynamics induced by IBRs. Due to the independence of external grid networks, conventional grid-following (GFL) inverters cannot support islanded operation and are more prone to destabilizing in weak grid conditions. To support a higher percentage of IBRs in the generation mix, recent studies have focused on emerging grid-forming (GFM) controls. The different characteristics of GFM and GFL control functions result in the known systems for GFL inverters not being directly applicable to GFM inverters. Thus, the design of GFM control should be carefully investigated prior to wide adoption. In this book chapter, the significant challenges related to the development of GFM control are discussed, and a detailed comparison between GFL and GFM control is presented. Furthermore, the asset- and system-level modeling of IBRs is discussed, and gray-box modeling is proposed to combine the advantages of both white- and black-box modeling. The application of GFM control in distribution systems is also discussed, and distributed secondary control is implemented for dynamic microgrids and system-level optimization using consensus algorithms. Finally, several methods are proposed to address overcurrent limiting, coordination among multiple assets, and system-level stability analysis toward facilitating the modernization of power grids. The goal of this book chapter is to clarify the roles and functions of GFM assets in modern power systems for grid resiliency enhancement.