Porto is served by a modern international airport, Francisco Sá Carneiro (IATA: OPO).
The airport is served by several international airlines, including low cost alternatives such as Ryanair and Easyjet. For a more detailed list of direct connections please see the aiport destinations page or the correspondent wikipedia section. You can also opt to travel through Lisbon, which has several regular daily flights to Porto.
The airport is located 11Km from the city, and is served directly by a subway station connecting you to the city centre through line E (a ticket from the airport to the city costs 1.85€ + 0.5€ for reusable Andante card). For more information about the subway check www.metrodoporto.pt. A taxi to the city centre will cost around 20€. For a more detailed list of options to go from the airport to the city check this page.