Adherens junctions are complexes that comprise E-cadherin molecules, which interact with each other on neighbouring cells, and with the underlying actin cytoskeleton at the apical surface of epithelia, to establish cell–cell contacts. These contacts are necessary for the maintenance of epithelial integrity but need to be disassembled to allow tissue remodelling and cell migration. Tsur et al. now show that the balance between adherens junction assembly and disassembly is regulated by the small ubiquitin-like modifier (SUMO) protein, which can be added to or removed from E-cadherin molecules. Specifically, they reveal that removal of the SUMO mark, mediated by a defined protease, is necessary for proper apical localization of E-cadherin and its interaction with actin, thus representing a key step in junctional assembly. Altogether, the authors uncover SUMO as an important modulator of adherens junctions. They suggest that SUMO molecules are constantly added to and removed from E-cadherin, thereby providing a mechanism to regulate adherens junction dynamics, which are crucial for morphogenesis and tissue homeostasis.