European Union (EU) nationals with a valid passport or identity card are permitted to work in Portugal without a visa and are entitled to the same rights as Portuguese nationals with regard to pay, working conditions and social security.
If entering to study, you may need to show proof that you are a student and have the means to support yourself.
If entering the country to work you may be asked to prove that you have adequate means to support yourself during your stay and that the cost of your return journey is secured.
An identity card (bilhete de identidade) must be carried at all times. Application forms are available from the Portuguese Consulate General. Contact the Consulate well in advance of departure to confirm requirements.
Employees must register at the Treasury to get a CIF number, without which their employer will not be able to pay them. More information (in Portuguese) is available from the Portuguese Ministry of Finance.
EURES - European Job Mobility Portal has a before and after moving to Portugal checklist that will help you to make sure you have completed all the essential tasks.