Anyone who has spent some time around children or philosophers will be famil-iar with the following situation: The child or philosopher will ask a why-questionand demand an explanation for the fact or phenomenon at hand. If lucky, onewill be able to produce an answer, albeit just to be confronted with a furtherwhy-question concerning that answer. Then, at some point of this game of why-questions and because-answers, it seems that the interrogee will have to admittheir ignorance, claim that at that point there is simply no explanation to be had,dare to spin around in a circle, or embark on an infinite regress and hope thattheir interlocutor tires before they do.The interrogee’s woes are likely exacerbated if the why-questions concernmatters like logical truths, modal and essential truths, explanatory or normativeprinciples, laws of metaphysics or nature themselves, certain axioms or first as-sumptions, and the existence of various special entities such as the empty set, theworld in its entirety or God, or even the existence of anything at all. Matters likethese can seem to be particularly stubborn when it comes to their explanation.For some of them, it may not be clear what shape an explanation could take evenin principle (sometimes the existence of anything at all is treated like this). Othersmay appear not to require an explanation, or it can even seem that asking for anexplanation is somehow misguided in such cases (for example, this has been sug-gested for essential truths). Finally, some of these truths may seem to demand aspecial, in some sense particularly strong, kind of explanation to do them justice.In a nutshell, the present book develops, explores, and applies a notion of ex-planation that promises some help for our unfortunate interrogee, namelyempty-base explanation.2While this idea is novel, it is located in the theoretical back-ground of several fundamental and tricky philosophical issues. With respect tothese, the investigation of empty-base explanation promises to improve our un-derstanding, helps to better assess existing accounts, and supplies us with promis-ing, novel approaches. To name but one example here, it will be argued thatempty-base explanation provides a convincing kind of ultimate or final explana-tion, i.e. an explanation that completely and conclusively explains a phenomenonwithout involving other phenomena for which further explanations could be demanded. As will be shown, the notion of empty-base explanation thereby has asignificant import for (amongst others) philosophical cosmology/theology (e.g. thecosmological argument), the debate about the principle of sufficient reason, andthe question of why there is anything at all.