In this thesis, I studied the diversification patterns of two groups of leaf mining Lepidoptera: Nepticulidae and Lithocolletinae (Gracillariidae). Both are found on all continents except Antarctica and are species-rich, but to different extents in different lineages and their centres of diversity are in different biogeographic regions, even though they predominantly feed on similar host plant families. The research I performed focused on comparing their species-level phylogenetic diversification patterns, based on a dataset that included the majority of their global diversity, to understand common factors that have driven their evolution.