The mouthpart structures of Endopterygota exhibit an extremely high diversity of form and function, yet they are composed of the same set of homologous components which are derived from arthropod limbs. Mouthpart features are prevalent in all studies of the high-level phylogeny of insects. Areas in which the phylogeny of Endopterygota has remained unresolved over the past decades concern the position of the Strepsiptera, the interrelationships of the orders of the Neuropterida, and the question of the sistergroup to the Siphonaptera. Paying attention to these unresolved internodes, the present review discusses current knowledge of mouthpart features and their value in deciphering the phylogeny of Endopterygota. Comprehensive comparative data for the mouthparts based on morphological studies have yet to be assembled and analysed in Endopterygota and their closest relatives. Providing such data would improve the hypotheses of the phylogeny of Endopterygota and could also contribute to a better understanding of mouthpart adaptation to various food sources.