Phytophagous insects dominate the terrestrial earth. While many are external plant feeders, a large diversity of insects specialize on feeding internally within plants. This study constructs one of the first phylogenies of the diverse leaf-mining moth superfamily Gracillarioidea, and examines broad patterns of life history evolution. This dissertation begins with a short introduction (Chapter 1), before a molecular phylogenetic analysis of the Gracillarioidea utilizing over 14,800 nucleotides (Chapter 2). Results indicate that 1) Douglasiidae probably does not belong in Gracillarioidea; 2) the phylogenetic position of Bucculatricidae in Gracillarioidea is generally weak, but strong when non-synonymous changes are analyzed alone; 3) deep divergences in the superfamily are difficult to resolve even with 21 genes; and 4) four strongly supported clades, roughly corresponding to Kumata's classifications were recovered in the Gracillariidae. Chapter 3 is a preliminary examination of life-history evolution in Gracillariidae, focusing on the "top down" effects from parasitoids that may have shaped the life histories of gracillariids. Results include: 1) larval traits (larval habit, cocoon ornamentation) is conserved on phylogeny, but traits associated with hosts are less so; 2) that host shifts in gracillariids are more common among closely related plants, and that closely related insects feed on closely related hosts; 3) blotch mining is the ancestral condition of mine form in Gracillariidae; 4) tentiform blotch mining, a modification of the simple blotch mine, may be an evolutionary innovation against parasitoids. The final three chapters focus on the taxonomy, life-history, and morphology of several gracillariids, including the description of three new species. The central theme is Phyllocnistis, a diverse, yet poorly studied serpentine mining gracillariid genus.