Everyone wishing to enter Israel must have a valid passport. The passport must be valid for a minimum of six months from the date of entry. Anyone who plans to visit an Arab country, with the exception of Egypt and Jordan, after entering Israel should request that the customs officer not stamp their passport.
Many countries, including the United States of America, have an agreement with Israel that allows their citizens to enter Israel as a tourist without a visa for up to 90 days. The full list of countries is available here.
For visits longer than 90 days, or to be eligible for employment in Israel, a separate visa is required. More information about visas is available here.