The search for alternatives to capitalism and the problem of comparative assessment of the performance of socialist and capitalist systems have inspired one of the richest and most remarkable episodes in the history of economic thought. By the mid 20th century an entire field had emerged, conceptualizing, theorizing, monitoring, and analyzing the largest and most consequential social and economic natural experiment in human history: Real-life Socialism. This research review focuses on the fundamental literature associated with the comparative study of socialist and capitalist systems. It features both a well-rounded inquiry of the modern history of economic thought, as well as a vibrant and critical disentanglement of the role of the economic system from the role of environment and policy decisions, as determinants of economic performance. This review will be an interesting and invaluable research resource for academics and students alike.