Generally not required for stays of up to 90 days per 180 days (visas are not required at all for members of EU or Schengen countries). Some nationalities need a Schengen visa.
The visa situation for entering Spain is as follows:
Citizens or residents of EU & Schengen countries No visa required.
Citizens or residents of Australia, Canada, Israel, Japan, New Zealand & the USA No visa required for tourist visits of up to 90 days out of every 180 days.
Other countries Check with a Spanish embassy or consulate.
To work or study in Spain A special visa may be required – contact a Spanish embassy or consulate before travel.