 The modern power system is transitioning away from synchronous machines and toward inverter-dominated systems, with large-scale penetration of renewable energy sources such as wind and solar. Traditional approaches to integrating these sources into the grid can cause frequency instability, which can be addressed by using inverters with virtual inertia control algorithms. These algorithms mimic the behavior of synchronous generators, allowing them to appear as such to the grid while maintaining system stability. This paper reviews the current state of the art in virtual inertia implementations, including their topologies and how they relate to synchronous generator dynamics. It also discusses the challenges and opportunities for future research. This article was authored by Ajwal Tamarkar, Deepesh Shrestha, Manisha Maharjan, and others.