Visas are required for a continuous stay of more than three months. But if your stay is shorter than three months you only need a valid passport.
As you might expect, all citizens of the EU countries can enter Switzerland without a visa for tourist purposes, and according to the official website, this 90 day rule applies to citizens of the following countries: countries of the American Continent (except Belize, Dominican Republic, Haiti, and Peru), Europe, Japan, Australia and New Zealand.
Here’s the full list: if you have a passport from one of the following countries, you do NOT need a visa for visit of up to 90 days in Switzerland:
Albania, Andorra, Antigua and Barbuda, Argentina, Australia, Austria, Bahamas, Barbados, Belgium, Bosnia and Herzegowina, Bulgaria, Brazil, Brunei, Canada, Chile, Costa Rica, Croatia, Cyprus, Czech Republic, Denmark, El Salvador, Estonia, Finland, France, Germany, Great Britain, Greece, Guatemala, Honduras, Hong Kong, Iceland, Ireland, Israel, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Macedonia, Macao, Malaysia, Malta, Mauritius, Mexico, Monaco, Montenegro, Netherlands, New Zealand, Norway, Nicaragua, Panama, Paraguay, Poland, Portugal, Romania, St.Kitts and Nevis, San Marino, Serbia, Seychelles, Singapore, Slovakia, Slovenia, South Korea, Spain, Suriman, Sweden, Taiwan, United States of America, Uruguay, Vatican, Venezuela.