Aspects of the evolution of the branchiopod crustaceans are reviewed and discussed. Despite views to the contrary presented in recent textbooks, the monophyly of Branchiopoda is defended based on morphological characters. The crown group Branchiopoda is supported/diagnosed by a set of synapomorphies relating to limb morphology of both larvae and adults, including, among others, a similar naupliar swimming/feeding apparatus, a similar development of trunk limbs, and a similar morphology of adult trunk limbs with six endites (number reduced later) and an unsegmented endopod. Phyllopodous limbs are among the most well-known features of Branchiopoda, but it is uncertain whether the phyllopodous nature of the limbs in itself can be considered a synapomorphy for this group, because the limbs of other crustaceans, both recent and fossil, also can be characterised as at least partly phyllopodous. Homologies of branchiopod trunk limbs to those of other crustaceans are discussed; based on similarities to trunk limbs of certain ‘Orsten’ fossils, it is concluded that the large, undifferentiated ‘corm’ of the limb most likely is an enlarged basis. Within Branchiopoda, strong evidence for a monophyletic Phyllopoda sensu Preuss (all branchiopods except anostracans) is presented. A monophyletic Diplostraca is also preferred based on morphological information, and the supporting characters for this group are listed. A remarkable branchiopod crustacean from the Devonian has recently been described with morphological features combining those of Notostraca and ‘Conchostraca’; it has major significance for the understanding of early branchiopod evolution. The question of a marine versus freshwater origin of Branchiopoda is discussed.