The question why people choose to vote or abstain in national elections has been extensively researched in the past decades. Yet, disagreement over what drives citizens to the polls persists. Literally, over a 100 different explanatory factors have been linked to the individual's decision to vote or abstain: ranging from individual characteristics like education, age and political interest, to socialization by friends and parents, to characteristics of the election-like political competition, and many more. Slowly, but surely, it has become difficult to see the wood for the trees. In the research project that we describe in this article, we wanted to take a step back and summarize where we stand and what we know about turnout. To this end, we carried out a meta-analysis of 90 empirical studies of individual-level voter turnout in national elections between 2000 and 2010. This allowed us to identify which variables are consistently linked to turnout, and which are not. In this article, we describe what meta-analysis is and give an example of how to carry out meta-analysis by describing our research project on turnout. [This content is provided in the format of an e-book.]