Caenogastropods comprise about 60% of living gastropod species and include a large number of ecologically and commercially important marine families. They have undergone an extraordinary adaptive radiation resulting in considerable morphological, ecological, physiological and behavioral diversity. While most are marine, the group also includes taxa that have independently radiated into freshwater and terrestrial habitats. This chapter reviews the fossil history and the higher systematics and phylogeny of this group, with emphasis on the areas of expertise of the authors. New analyses involve a morphological data set, which includes ultrastructural data, and a combined analysis with the molecular data sets from earlier analyses.