Getting to Yap requires planning and patience. There are no direct flights from most of the world, and the air service is thin enough that missing a connection can cost you days. The main gateway is Guam, which has United Airlines flights onward to Yap on the carrier's "island hopper" route — a single aircraft that threads east through Chuuk, Pohnpei, and Kosrae before turning back west to Palau via Yap. The island hopper runs a few times per week and the schedule shifts seasonally, so check United's current timetable before building an itinerary around it.
From Palau there is also occasional air service to Yap, which makes a logical pairing if you are diving both destinations. Flying via Tokyo or Manila is possible for travellers coming from Asia or Europe, connecting through Guam. There is no sea ferry service. Yap's Airport (YAP) is small — a single runway, no jetbridge — but handles everything that comes in, and the immigration and customs process is straightforward for US passport holders (Yap is part of the Compact of Free Association with the United States, so Americans enter without a visa). Citizens of most other countries can enter visa-free for up to 30 days; check current requirements for your passport.