APA (7th ed.) Citation

Knorr, K. E., & Verba, S. (1961). The international system: Theoretical essays. Princeton University.

Chicago Style (17th ed.) Citation

Knorr, Klaus E., and Sidney Verba. The International System: Theoretical Essays. Princeton: Princeton University, 1961.

MLA (9th ed.) Citation

Knorr, Klaus E., and Sidney Verba. The International System: Theoretical Essays. Princeton University, 1961.