While research designs can be distinguished along various dimensions, we all face the same set of core research design issues. What is a relevant research problem? How can I improve concepts and measurements? Which and how many variables and cases should I select? How can I evaluate rival explanations and which theoretical conclusions can I draw from my research? Which evidence would lead me to reject and reformulate my initial theory? This volume was written to help advanced students of political science and their neighboring fields to think about these issues and come up with practical solutions for their own research. It turns out that the distinction between qualitative and quantitative research is often inadequate. Some solutions to research design problems are common to both types of research; others cross-cut the traditional qualitative-quantitative divide. Moreover, every solution has its strengths and weaknesses and, therefore, involves substantial trade-offs along the way.