Due to the particular confinement and reduced dimensionality of quantum rings, Coulomb interaction plays an important role for their electronic structure. In this chapter, we discuss the dependency of the ground state of an idealized quantum ring contained a small number of interacting electrons on geometric parameters like ring radius, radial confinement and eccentricity. The ring geometry affects both the charge distribution and the spin configuration in a quantum ring. Numerically exact results obtained from path-integral quantum Monte Carlo demonstrate the strong connection between the structure and the total spin of the ground state emerging from the interplay between confinement and Coulomb interaction.