Athens International Airport Eleftherios Venizelos (IATA: ATH, ICAO: LGAV), commonly initialised as AIA, is the largest international airport in Greece, serving the city of Athens and region of Attica. It began operation on 28 March 2001 (in time for the 2004 Summer Olympics) and is the main base of Aegean Airlines, as well as other smaller Greek airlines. It replaced the old Ellinikon International Airport.

Athens International Airport is currently a member of Group 1 of Airports Council International (over 25 million passengers). As of 2024^[update], it is the 16th-busiest airport in Europe and the second busiest and second largest in the Balkans, after Istanbul Airport.

The new Athens International Airport covers an expanse of 16,000 acres (25.0 sq mi; 64.7 km²), making the facility among the largest in Europe and in the world in terms of land area.

AIA is located between the towns of Markopoulo, Koropi, Spata and Loutsa, about 20 km (12 mi) to the east of central Athens (30 km (19 mi) by road, due to intervening hills). The airport is named after Elefthérios Venizélos, the prominent Cretan political figure and Prime Minister of Greece, who made a significant contribution to the development of Greek aviation and the Hellenic Air Force in the 1930s.^{[citation needed]} As to-date, the airport is operated by AIA S.A. and ownership is divided between the Hellenic Republic (Greek State) and Private Sector in a 55%-45% stake following a PPP scheme for the airport company. Currently, private investors include the Copelouzos Group (5%) and PSP Investments of Canada (40%), following purchase of Hochtief's shares.

The airport was constructed to replace the now-closed Athens (Ellinikon) International Airport, as the latter had reached its saturation point with no physical space for further growth. Studies for a new airport had been carried out from as early as the 1970s, with as many as 19 different locations being looked at before an area close to the town of Spata was chosen as suitable. Athens Airport SA, a state-owned company, was established in 1978 to proceed with the plans. However, after delays and slow development, the project was revived in 1991, approximately 1 year after the city lost the right to host the 1996 Summer Olympics to Atlanta, USA and the possibility of submitting a bid for the 2000 Game was discussed. However, the city presented the project that was eventually the winner for the 2004 Summer Olympic Games, with the then government launching an international tender for the selection of a build-own-operate-transfer partner for the airport project, with Hochtief of Germany being selected.

In 1996, Athens International Airport S.A. (AIA) was established as a Public–private partnership with a 30-year concession agreement. That same year, the €2.1 billion development finally began with an estimated completion date of February 2001. The airport construction was completed five months before schedule, but was delayed opening a month due to surface connections to Attiki Odos not being completed. The airport officially opened on 28 March 2001. Its major features include two parallel runways being 4 km (2.5 mi) and 3.8 km (2.4 mi) long respectively. The airport has received approval from the European Aviation Safety Agency and the Federal Aviation Administration for take-offs and landings of the biggest passenger jet worldwide, the A380. The first ever A380 to visit 'Eleftherios Venizelos' Athens International Airport made an emergency landing on 13 April 2011 for emergency medical reasons. The first scheduled A380 flight took place on 26 October 2012 by Emirates.

The Greek government-debt crisis reduced the overall passenger traffic of the airport for six consecutive years. Many long-haul airlines outright terminated service to the airport, while others chose to operate on a seasonal basis only, opting to terminate service during the winter months. Moreover, these problems were further exacerbated by the closure of Olympic Airlines, which operated many long-haul flights to and from the airport. In 2013, the airport handled just above 12.5 million passengers, 3.2% fewer than in 2012 and lower by approximately 25% when compared to 2007's traffic, which was the all-time-high at that time.

2014 signaled a strong recovery for the airport's passenger traffic. More than ten new airlines started new flights to and from Athens. Aegean Airlines strengthened its network by 30% (with many more destinations scheduled for 2015) while Ryanair established a new base in the Athens Airport and added eight destinations. During 2014 the airport operators reported a passenger traffic volume of 15.1 million passengers, an increase of over 21%. This was the result of new destinations, and capacity increases on existing routes, such as the resumption of flights by Singapore Airlines and Gulf Air, and the decision by Emirates, Etihad Airways and Qatar Airways to fly more frequently to and from Athens. Delta Air Line resumed their weekly flights and American Airlines retained their seasonal schedules to/from USA with even more frequent connectivity. From 2017 onwards, year-round services to Singapore were scheduled to resume after more than five years, with flights operated by Scoot.