Spain is a party to the Schengen agreement. As such, U.S. citizens may enter Spain for up to 90 days for tourist or business purposes without a visa. The passport should be valid for at least three months beyond the period of stay.
Although European Union regulations require that non-Eu visitors a stamp in their passports upon initial entry to a Schengen country, many borders are not staged with officers carrying out this function. If an American citizen wishes to ensure that his or her entry is property documented, it may be necessary to request a stamp at an official point of entry. Under local law, travelers without a stamp in their passports may be questioned and asked to document the length of their stay in Schengen countries at the time of departure or at any other point during their visit, and could face possible fines or other repercussions if unable to do so.
Please note that non-U.S. passport holders are responsible for obtaining the required documentation applicable for their entry.