Ryanair is an Irish ultra low-cost airline group headquartered in Swords, County Dublin, Ireland. The parent company, Ryanair Holdings plc, includes subsidiaries Ryanair DACTooltip Designated activity company, Malta Air, Buzz, Lauda Europe and Ryanair UK. Ryanair DAC, the oldest airline of the group, was founded in 1984. Ryanair Holdings was established in 1996 as a holding company for Ryanair with the two companies having the same board of directors and executive officers. In 2019, the transition began from the airline Ryanair and its subsidiaries into separate sister airlines under the holding company. Later in 2019, Malta Air joined Ryanair Holdings.

Ryanair has been characterised by its rapid expansion, a result of the deregulation of the aviation industry in Europe in 1997 and the success of its low-cost business model. The group operates more than 600 planes. Its route network serves over 40 countries in Europe, North Africa (Morocco) and the Middle East (Israel, Jordan and Turkey). The primary operational bases are at Dublin, London Stansted and Milan Bergamo airports. Ryanair is Ireland's biggest airline, and in 2016, became the world's largest airline by scheduled international passengers. Almost all aircraft in the group's fleet are Boeing 737s.

The company has at times been criticised for its refusal to issue invoices for the VAT-exempt services it provides (airfares), poor working conditions, heavy use of extra charges, poor customer service, and tendency to intentionally generate controversy in order to gain publicity.

Since its establishment in 1984, Ryanair has grown from a small airline, flying the short journey from Waterford to London Gatwick, into Europe's largest carrier. There have been over 19,000 people working for the company, most employed and contracted by agencies to fly on Ryanair aircraft.

The airline went public in 1997, and the money raised was used to expand the airline into a pan-European carrier. Revenues have risen from €640 million in 2003 to €4.66 billion in 2010. Similarly, net profits have increased from €48 million to €339 million over the same period.^{[citation needed]}

Ryanair was founded in 1984 as Danren Enterprises by Christopher Ryan, Liam Lonergan (owner of Irish travel agent Club Travel), and Irish businessman Tony Ryan, founder of Guinness Peat Aviation. The airline was shortly renamed Ryanair on 8 July 1985. It began operations in 1985 flying a 15-seat Embraer Bandeirante turboprop aircraft between Waterford and Gatwick Airport.

The first chief executive was Eugene O'Neill (1956–2018), who had formerly worked as managing director of Ryan's Sunday Tribune newspaper and as Ryan's personal assistant. O'Neill was talented at marketing but did not focus on costs, and the airline lost money in its early years. Ryan vetoed O'Neill's proposal to take Aer Lingus to the European Commission for breach of competition rules, because at the time Aer Lingus was state-owned and Ryanair depended on the Irish government for its route licences. Ryan sacked O'Neill in September 1987, who sued for wrongful dismissal.

In 1986, the company added a second route from Dublin to Luton with two Hawker Siddeley HS 748s, thus directly competing with the Aer Lingus/British Airways duopoly for the first time. Under partial European Economic Community (EEC) deregulation, airlines could begin new international intra-EEC services as long as one of the two governments approved (the so-called "double-disapproval" regime). The Irish government at the time refused its approval to protect Aer Lingus, but Britain, under Margaret Thatcher's deregulating Conservative government, approved the service. With two routes and two aircraft, the fledgling airline carried 82,000 passengers in one year.