This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book shows how the mixed methods research strategy can be productively utilised in the discipline of criminology and criminal justice. Mixed methods are a relatively new methodological strategy, which has become increasingly prominent over the last three decades or so, and in particular since the turn of the 21st century. The book focuses on the use of mixed methods within the discipline of criminology. Mixed methods are becoming increasingly prominent in criminology. It considers Ethics, and the importance of undertaking ethical practice in mixed methods criminological research. The book discusses the epistemological and ontological underpinnings of mixed methods research. It provides a thorough overview of the evaluative terms associated with the quantitative strategy and qualitative strategy, which should be applied to the inferences generated by each component.