Although—following contemporary interpreters—this article qualifies Theodore de Régnon's famous sharp distinction between Eastern and Western trinitarianism, it argues that the 'acid test' of the liturgy makes clear that there simply is a contrast between Eastern and Western ways of conceiving of the Trinity. Historically, this contrast found its focal point in the filioque controversy. Therefore, after a sketch of the broader framework of the divergence between Eastern and Western theology, the pros and cons of the addition of the filioque clause to the Creed are discussed. It turns out that Augustine played an ambivalent role in this connection. Finally—drawing on some recent proposals, a way forward in the filioque debate is suggested.