The solid-liquid interface is an essential facet of heterogeneous chemistry. While the attempt to theoretically understand the solid-liquid interface was started by Helmholtz more than 100 years ago, the atomistic insights of solid-liquid interactions are still rarely investigated due to the high computational costs. Consequently, the impact of the liquid on the properties of the solid is often ignored or simplistically incorporated into computational models. However, incorporating the liquid phase can significantly improve the theoretical accuracy of the properties of the solid-liquid interface. In addition, the solid-liquid interface is influenced by several compounding factors like pH, electrolytes, and surface charge. To address these challenges, density functional theory (DFT)-based simulations became the most popular approach due to the affordable computational cost and relatively high accuracy. In this chapter, the principles and methodologies of DFT-based simulations will first be introduced. After that, some recent studies on interfaces between different solids and water will be discussed as model systems to show the unique advantages and disadvantages of DFT-based simulations.