If your passport describes you as a British Citizen or a British Subject with Right of Abode in the United Kingdom, you don't need a visa to enter Spain. If you have another type of British nationality, you should check entry requirements with their nearest Spanish Embassy or Consulate. read more
For U.S. citizens heading to Spain, proper documentation is the key to an easy border crossing. You always need a passport, but you might need a visa too. read more