To obtain a Spanish passport, you must be a Spanish citizen, following which you may apply for a Spanish passport through either the foreign embassy in the country you live in, or if you are Spanish and live in Spain, you apply through your own government offices. You need proof of your Spanish citizenship, passport photos and a check for a small fee. The passport must be applied to in person at your closest Spanish Consulate or embassy. Both Spain and the U.S. recognise dual citizenship (Spain recently in 2002) and therefore it is possible for you to hold two passports if you can claim citizenry.
Acquire Spanish citizenship. You can receive citizenship either through marriage, parentage or adoption, or five years of residency as a political refugee (two years for citizens of Latin American, Andorra, Philippines, Equatorial Guinea and Portugal). You cannot apply for a passport without proof of Spanish citizenship. For more information on who qualifies for Spanish citizenry and how to obtain it, visit euskosare.org.
Make an appointment with the Spanish embassy or Spanish Consulate General that has jurisdiction over your geographical region. You must go in person to apply for the passport. Passport applications cannot be made through mail or online with the embassy. For a list of Spanish Consulate Generals and Embassies, please refer to the resources below titled "Spanish Consulate Locations" to determine which location you must apply through.
Gather all of the required documents. At your appointment, you must have with you two passport photos and proof of your Spanish citizenship (either a birth certificate, Spanish National Identity Card, and possibly the birth certificates of your parents).
Pay the passport application fee. As of 2009, the fee is 20 Euros ($30 U.S.), and must be paid at time of application in either cash or check. When your passport has been approved, it will be sent to you in the mail.