Citizens of the U.S.A., Canada, and Mexico are not required to have a visa to visit the Czech Republic/Schengen area for a period of up to 90 days within a 180-day period (except profitable activities) - it is calculated from the date of first entry into any Schengen country.
However, visas are required for stays exceeding 90 days and profitable activities. The conditions of entry and short term stay of aliens in the territory of the Czech Republic/Schengen area are regulated by the Regulations No 810/2009 of the European Parliament and of the Council, so called "Visa Code" and for long term visa by the Act No. 326/1999 Coll. Citizens of EU countries, EEA countries and citizens of Switzerland do not require a visa for any type of visit or stay in the Czech Republic as effective on May 1, 2004.