The Oxford Handbook of Political Methodology is designed to reflect developments of all the key specific methodologies through comprehensive overviews and critiques. Political methodology has changed dramatically in the past thirty years. Not only have new methods and techniques been developed, but the Political Methodology Society and the Qualitative Methods Section of the American Political Science Association have engaged in on-going research and training programs that have advanced both quantitative and qualitative methodology. This Handbook emphasises three things. First, techniques should be the servants of improved data collection, measurement, conceptualization, and the understanding of meanings and the identification of causal relationship in social science research. Techniques are described with the aim of showing how they contribute to these tasks, and the emphasis is upon developing good research designs — not upon simply using sophisticated techniques. Second, there are many different ways that these tasks can be undertaken in the social sciences through description and modelling, case-study and large-n designs, and quantitative and qualitative research. Third, techniques can cut across boundaries and be useful for many different kinds of researchers. The articles ask how these methods can be used by, or at least inform, the work of those outside those areas where they are usually employed. For example, scholars describing large-n statistical techniques should ask how their methods might at least inform, if not sometimes be adopted by, those doing case studies or interpretive work, and those explaining how to do comparative historical work or process tracing should explain how it could inform those doing time-series studies.