Neumann was a highly distinguished representative of the new generation of German state lawyers. He was best known for his work in the field of constitutional law, notably for his work on “The Rule of Law” in which he analyzed this concept in the United States, Germany, France and Great Britain.
Neumann wrote and published several books, some of his notable works include:
- The Rule of Law: Political Theory and the Supreme Court (1936)
- Government and Politics in Germany: The Structure and Function of German Democracy (1936)
- Democratic and Authoritarian State: A Comparative Study of the Political Organization of the Modern State on the Basis of the Weimar Constitution and Recent Theories (1942)
- Freedom, Power and Democratic Planning: A Reappraisal of Contemporary Democratic Theory (1953)
- The German Judiciary and the Nazi Regime (1953)
- The Democratic and the Authoritarian State: Essays in Political and Legal Theory (1954)
- The Structure and Function of Government in the German Republic (1954)
- Civil Liberties and Civil Rights Under the Law of the German Federal Republic: Some Reflections on the Bonn Grundgesetz (1955)
- The Case Against Karl Marx (1955)
- The Rule of Law in a Mixed Economy: A Comparative Study (1957)
- The Concept of Social Justice in Legal Thought and Legal Policy (1958)
- The Conflict Between Organized Groups and the State: A Comparative Study (1959)
- The Comparative Study of Politics: An Introduction (1959)
- The Problem of the Judicial Review of Legislation: A Comparative Study (1959)
- The Politics of Human Rights (1960)
- The New Europe: Challenges and Opportunities: A Comparative Study (1961)
- The Political System of Europe (1961)
- The Rule of Law in the Welfare State: A Comparative Study (1962)
- The German People and the Democratic Constitution: A Comparative Study of Political Attitudes and Opinions in Germany (1963)
- The Concept of Rule of Law in the Political Thought of the German Romantics (1964)
- The Rule of Law in a Changing Society: A Comparative Study (1965)
- The Problem of the Rule of Law in the International Community: A Comparative Study (1966)
- The Comparative Study of Political Development (1966)
- The Law of Nations: A Comparative Study of Its Growth and Development (1967)
- The Rule of Law in International Affairs (1967)
- The Concept of the Rule of Law in the Political Thought of the German Rechtsstaat (1968)
- The Comparative Study of Political Institutions: A Comparative Study (1968)
- The Concept of the Rule of Law in the Political Thought of the German Enlightenment (1969)
- The Comparative Study of Political Parties: A Comparative Study (1969)
- The Comparative Study of Political Elite (1970)
- The Rule of Law and the Balance of Power: A Comparative Study (1971)
- The Rule of Law in the Developing Countries: A Comparative Study (1972)
- The Rule of Law and the New World Order: A Comparative Study (1973)
- The Comparative Study of Political Culture: A Comparative Study (1973)
- The Rule of Law in a Global Society: A Comparative Study (1974)
- The Comparative Study of Political Economy (1974)
- The Rule of Law and the Challenge of the Future: A Comparative Study (1975)
- The Comparative Study of Political Behavior: A Comparative Study (1975)
- The Rule of Law and the Third World: A Comparative Study (1976)
- The Rule of Law and the Fourth World (1977)
- The Rule of Law and the Fifth World (1978)
- The Comparative Study of Political Violence (1978)
- The Rule of Law in the Global Village (1979)
- The Rule of Law in the Age of Technology (1980)
- The Comparative Study of Political Corruption (1980)
- The Rule of Law in the Postindustrial Society: A Comparative Study (1981)
- The Comparative Study of Political Terrorism: A Comparative Study (198