Some disagreements concern our most fundamental beliefs, principles, values, or worldviews, such as those about the existence of God, society and politics, or the trustworthiness of science. These are ‘deep disagreements’. But what exactly are deep disagreements? This paper critically overviews theories of deep disagreement. It does three things. First, it explains the differences between deep and other kinds of disagreement, including peer, persistent, and widespread disagreement. Second, it critically overviews two mainstream theories of deep disagreement, the Wittgensteinian account and (...) the Fundamental Epistemic Principle account, before introducing a Hybrid account. Finally, it explores the notion that deep disagreements can be deeper than others. (shrink)