Participants from EU-EFTA-countries:
You will not need a visa to enter Switzerland, visit: https://www.bfm.admin.ch/content/dam/data/migration/einreise/merkblatt_einreise/mb-grueezi-e.pdf
Participants from other countries:
Please refer to the list over the link to determine if you need a visa to enter Switzerland: https://www.bfm.admin.ch/content/dam/data/bfm/rechtsgrundlagen/weisungen/visa/bfm/bfm-anh01-liste1-e.pdf
Your visa application should be made to the Swiss consular authorities in your country. Addresses of all the Swiss representations/consular services can be found here: http://www.eda.admin.ch/eda/en/home/reps.html .
An official invitation can be sent to the participants on demand (contact: firstname.lastname@example.org). Participants have to start their visa application process early, at the latest 1 month prior to the workshop.