James M. Buchanan (1919-2013) contributed significantly to the understanding of political and social processes through his works. He always started from the premise of individual freedom, which must be protected. This compendium presents the political economist and his relevant ideas that are significant for understanding political decisions. The introduction and afterword discuss the person, his work, and particularly the political relevance of his contributions. Both the analytical insights and the proposals for designing constitutional orders that protect individual freedom are addressed. The focal points of the compendium include: methodological individualism, public choice, contract theory, constitutional theory, public goods, justice, and state finances. In doing so, the editors provide a pointed look at the most important theses and ideas.