From within Europe, you'll have no problems entering Portugal by land or air. If arriving from further afield, check if you need a Visa before arrival.
Tourists that come from countries under the Schengen Agreement only need their Identification Card to travel. Tourists from other countries need a passport to stay in the country for no more than 3 months (2 months for American and Canadian nationals). A Visa is required to stay for any other length of time in Portugal. To extend a Visa or 90-day period of stay after arriving in Portugal, contact the Foreigners' Registration Service (major tourist towns also have branches). Visitors to Portugal should be able to produce onward travel arrangements and proof of sufficient funds to support their holiday.
As regulations can change overnight, we recommend that you contact a Portuguese Embassy/Consulate to obtain complete and updated information.