  We generalize principal bundles and quotient stacks to the two-categorical
context of bisites. We introduce a notion of principal 2-bundle that makes
sense for a 2-category with finite flexible limits, endowed with a bitopology.
We then use principal 2-bundles to explicitly construct quotient-pre-2-stacks,
which are the analogues of quotient stacks one dimension higher. In order to
perform this construction, we prove that principal 2-bundles are closed under
iso-comma objects and we restrict ourselves to (2,1)-categories. Finally, we
prove that, if the bisite is subcanonical and the underlying (2,1)-category
satisfies some mild conditions, quotient pre-2-stacks are 2-stacks.
