Detailed information can be found on the Spanish page.
Do I need an airport transit visa?
For other nationalities, please refer to the list on the webpage of the State Secretariat for Migration (SEM).
If you are obliged to hold an airport transit visa (yes), please apply for it and refer to the information on the webpage:
If you are not obliged to hold an airport transit visa (no/your country is not mentioned in the list on the SEM webpage), you are allowed to transit through Switzerland and stay in the airport international transit area without any visa.