This Review of Chemistry Education Research (CER) provides an overview of the development of research in chemistry education from the early days, when ideas about how to teach chemistry and help students learn were guided by practitioner wisdom, to current research that is based on theories of learning and provides evidence from which to make arguments about improving teaching and learning. We introduce the dominant learning theories that have guided CER over the years and attempt to show how they have been integrated into modern research in chemistry education. We also provide examples of how this research can be used to inform the development and use of educational materials. Because CER literature is vast, we chose to limit the research we reviewed to those studies that help us answer three driving questions: (1) What should students know and be able to do with that knowledge? (2) How will we know that students have developed a coherent and useful understanding of chemistry? (3) What evidence do we have about how to help students develop a deep and robust understanding of chemistry?