Dictyostelids were once grouped with fungi because their fruiting structures are superficially similar. However both protists evolved quite distinct strategies to reach this mode of species propagation. This chapter describes the cell communication systems that cause Dictyostelid amoebas to aggregate and that regulate cell-type specialization and cell movement during fruiting body formation. It also highlights how increasingly complex morphologies appeared during dictyostelid evolution and how some of these morphological innovations were caused by modification of specific cell–cell signalling systems.