Understanding how development and ecology shape organismal evolution is a central goal of evolutionary developmental biology. This chapter highlights a class of traits and organisms that are emerging as new models in evo-devo and eco-devo research: beetle horns and horned beetles. Horned beetles are morphologically diverse, ecologically rich, and developmentally and genetically increasingly accessible. Recent studies have begun to take advantage of these attributes and are starting to link the microevolution of horned beetle development to the macroevolution of novel features, and to identify the genetic, developmental, and ecological mechanisms, and the interactions between them, that mediate organismal innovation and diversification in natural populations. Here, I review the most significant recent findings and their contributions to current frontiers in evolutionary developmental biology.