There are really just two ways to get to the islands, by ferry or by plane. Although, you will need to jump on a ferry to get to Formentera. The biggest airport is on Mallorca, serving between 20 and 30 million traveler's from more than 50 airlines every year. Ibiza and Menorca both offering regular flights during the summer season from larger destinations of Europe.
If you are looking to bring your own car or just want to experience different ways of travel, there are many ferries from mainland Spain as well as neighbouring countries during the week.