Från usembassy.gov :
A. Effective December 30, 2008, Maltese citizens are eligible to travel to the U.S. without a visa under the Visa Waiver Program if the following conditions are met:
- The visit is less than 90 days
- The visit is for tourism or business
- The traveler holds a valid biometric passport
- The traveler registers for and receives an approved travel authorization, or ESTA (Electronic System for Travel Authorization), by entering their travel details at https://esta.cbp.dhs.gov at least 72 hours prior to commencing travel
- The traveler has a valid return ticket
- The traveler has no prior legal convictions.