The taxonomy of the green algal genus Dunaliella is often seen as confusing and the names associated with species in culture collections are sometimes suspect. This paper evaluates and reviews the current taxonomy based on morphological and biochemical characters of this genus. The life history of Dunaliella is also presented. The variability, stability and usefulness of the main characters used to characterise the taxa are evaluated, based both on the literature and on a detailed examination of the Dunaliella strains in the Murdoch University Microalgae Culture Collection. A detailed updated description and key to the 22 species and a number of varieties and forms of the marine and halophilic species of Dunaliella currently recognised is given to allow researchers to identify their strains.