Symbiotic associations with microbes are important driving forces of evolutionary innovation. The megadiverse insect order Coleoptera, the beetles, are associated with an astounding diversity of symbionts that provide a wide range of functional benefits to their hosts. Highlighting a few selected beetle-microbe associations, I will report on novel findings of symbiont-provided defense, microbe-enabled digestion of plant material, and symbiont-mediated adaptation to the abiotic environment. These examples are intended to show the impact of symbionts on niche expansion and diversification in beetles, but also provide insights into life-style switches from parasitism to mutualism in bacteria as well as the process of extreme genome reduction beyond the well-known intracellular symbioses. Furthermore, we managed to introduce a genetically tractable intracellular bacterium into one of our experimental model beetles that now allows us to study the molecular basis of symbiosis establishment as well as the interaction between the newly introduced bacterium and the ancient endosymbiont. The results provide interesting first insights into the molecular host-symbiont interplay as well as the evolutionary steps leading to the establishment of novel symbioses.