Art. 27 of the Swiss Citizenship Act (SCA) provides that anyone who has lost Swiss citizenship may apply for reinstatement of citizenship within 10 years and, after the expiry of that period, anyone who has resided in Switzerland for three years may apply to have their Swiss citizenship reinstated.
For example, if a female Swiss citizen lost her Swiss citizenship
by marrying a foreign national before 1 January 1992;
through forfeiture: i.e. because they were born abroad, the Swiss representation was not notified within the prescribed period, and the birth was not registered in the Swiss civil register;
through relief of citizenship;