Abstract: Action languages allow for a concise representation of actions and their effects while at the same time being easily readable and writable for humans. In this paper, we introduce ${\mathcal D}$, the first action language that centres around default reasoning about actions and change. It allows to specify normal Reiter-style defaults and provides a semantics that has at its core the groundedness of conclusions. This is not only of use for default conclusions, but also for ${\mathcal D}$'s solution to the ramification problem. Additionally, our language does not suffer from Yale Shooting-like counterexamples since it uses different mechanisms for default persistence and default change. The answer set programming paradigm is used as the basis of ${\mathcal D}$'s implementation, which we prove sound and complete with respect to the language's semantics. We finally present a showcase application for the language: its straightforward solution to the qualification problem.