Cell adhesion requires dynamic links between adherens junctions in the plasma membrane and the underlying cytoskeleton. Catenin proteins that associate with cadherins in these junctions lie at the heart of this connection, and there is much interest in the structural basis of how the α-catenin subunit mediates communication between F-actin and the β-catenin–cadherin complex. Here, Tepass and colleagues assess which domains of α-catenin are required for normal adherens junction integrity and cell adhesion in Drosophila melanogaster. They analyse the functional consequences of expressing mutant or fusion proteins that separate α-catenin function from β-catenin association and the effects of α-catenin oligomerization states. Their results support a model in which monomeric α-catenin mediates the essential link between the β-catenin–cadherin complex and F-actin, whereas dimeric α-catenin provides a cytoplasmic pool for subunit exchange.