Due to the high abundance and low cost of sodium (Na), Na-ion batteries (NIBs) have emerged as a promising candidate for medium- and large-scale stationary energy storage. To date, NIB research has focused on understanding and optimizing the electrode materials, electrolytes, and their interfaces. This chapter focuses on atomic-scale studies of NIB electrolytes. The different electrochemistry and properties of the NIB electrolytes require employment of different computational methods. In common for all NIB electrolytes is the need to computationally evaluate and predict the ionic conductivity and Na+ ion diffusion mechanisms. Two major molecular modeling techniques have been applied: quantum-mechanics-based density functional theory (DFT) methods and statistical-mechanics-based molecular dynamics (MD) methods. At the smallest length and time scale, DFT has been used to solve the time-independent Schrödinger equation to obtain a complete quantum mechanical description of practical model systems. MD and ab initio molecular dynamics simulations are used to model the dynamic properties of electrolytes such as diffusivity and ionic conductivity.