Armadillo (Arm) repeat proteins contain tandem copies of a degenerate protein sequence motif that forms a conserved three-dimensional structure. Animal Arm repeat proteins function in various processes, including intracellular signalling and cytoskeletal regulation. A subset of these proteins are conserved across eukaryotic kingdoms, and non-metazoa such as Dictyostelium and Chlamydomonas possess homologues of members of the animal Arm repeat family. Higher plants also possess Arm repeat proteins, which, like their animal counterparts, function in intracellular signalling. Notably, these plant Arm proteins have novel functions. In addition, genome sequencing has identified a plethora of Arm-related proteins in Arabidopsis.