Secession (independence) usually means when part of one country declares its independence and breaks away or leaves that country to start a new country.

Constitutions of countries may include articles that either legally forbid or allow secession of part of the country. Most national constitutions, which have articles about secession, forbid it, but a few constitutions, such as the constitutions of the former Soviet Union, the former Yugoslavia, and Ethiopia allow the secession of their republics.

A secession attempt might be violent or peaceful.