The Two Nations theory can refer to:
- Two-Nation Theory, the view that Muslims and Hindus in Colonial India were separate nations
- Two nations theory (Ireland), the view that the Northern Ireland Protestants are a distinct Irish nation
- Deux nations or Two Solitudes (Canadian society), the view that French and English Canada are separate nations
- One Country on Each Side, the view that the People's Republic of China and the Republic of China (or alternatively, Taiwan itself) are two different countries, (namely "One China, one Taiwan"), as opposed to two separate political entities within the same country of "China".