Abstract: Strong approximation is a technique in arithmetic geometry to find a k-point of a variety over a number field which is v-adically close to a finite number of local points. It is desirable to understand what the obstructions to strong approximation are and when they vanish. In this talk we will review several important concepts of strong approximation before then showing how one is able to extend these ideas from varieties to algebraic stacks. We will then apply these concepts to BG, the classifying stack of G-torsors, and see that the etale-Brauer-Manin obstruction is the only obstruction in this case.