Flights to Europe
Most international airlines fly to Schiphol airport in Amsterdam. However, low cost internal flights in Europe mean that it could be cheaper to fly to London, then fly onto Amsterdam on a "bucket shop" flight.
Barcelona airport is eight miles from the city. It has three terminals. Terminal A is for foreign airline departures and international arrivals, while terminal B is used for Spanish airline departures and arrivals from the European Union.
Flying into Ireland from the UK is easy. Aer Lingus, the national carrier of the Republic operates from nine airports in the UK and nine cities across Europe. Dublin, Cork and Shannon are all only an hour from the UK. Dublin is the main airport for the Republic. There is a frequent bus service from the airport to the city centre.
Paris has two airports, both of them outside the city Charles de Gaulle (also known as Roissy) is about 26 kilometres from the city centre. To get out of the airport and into the city, catch the RER train to Gare du Nord, or Chatelet. There are shuttle buses from terminal 1 to the RER station. You can get to the station directly from terminal 2. Air France runs a bus service to the city centre that leaves every 15 minutes.
Ibiza Airport is a 20 minute drive from Ibiza Town, and there are hourly buses that run from the airport to the capital. Many airlines fly to Ibiza, or have flights that go via Madrid or Barcelona. Expect flight prices to go up, and availability to drop the deeper you are into peak season (June, July and August.) Go and British Midland do cheap flights from the UK.
Otherwise you could get a flight to Barcelona or Valencia, and from there get a ferry to Ibiza, or book an onward flight. Iberia fly frequently from Barcelona to Ibiza.
This is going to be your only option if you are arriving from North America, Australia & New Zealand, as there are no direct flights to Ibiza from those countries. There are however plenty of airlines which can get you to the major Spanish cities, from where you can catch a connecting flight to the island.