This entry surveys the phonological asymmetries between roots and non‐roots (affixes, clitics). It starts with an extraphonological, structural definition of roots, and considers those non‐phonological properties that are phonologically relevant: they are easily borrowed, and they are most deeply embedded. The empirical portion of the entry concentrates on templaticism and size restrictions, asymmetries in segmental contrast/inventories, the properties of multiroot words (compounds) and accentual characteristics that differ between roots and affixes. The theoretical section surveys theories that account for these properties: Prosodic Morphology, Positional Faithfulness, the cycle and its analogs and Anti‐Faithfulness. The entry then critically reviews several recent and not‐so‐recent proposals that blur the line between affixes and roots, using the ‘root’ designation diacritically or recasting diacritic distinctions as structural distinctions. The concluding section discusses the role of roots in phonological learnability.