The goal of this class is to familiarize students with some of the core methods used by political scientists to make causal inferences using quantitative data. We will cover both experimental and observational methods that can be deployed to test theories. For each approach we will consider their strengths and limitations. Much of what we will discuss in this class will surely be frustrating as the material will expose the difficulty of making credible inferences about much of what we care about. Still, a deep understanding of the issues that emerge when we seek reliable answers to hard questions will also make students appreciate the relatively slow progress of our discipline.