Longyearbyen is served by Svalbard Airport (LYR), which sits just a couple of kilometres from the town centre. Direct flights operate from Oslo (approximately 3 hours) and Tromsø (approximately 1.5 hours), with Norwegian and SAS running regular services. During peak season flights run almost daily; in the quieter winter months there are still several per week.
No visa is required for most nationalities — the Svalbard Treaty grants visa-free access to citizens of all signatory states. However, you will need adequate travel insurance that covers medical evacuation, as the nearest major hospital is in Tromsø.
For trip planning and guided expeditions, the Svalbard Wildlife Service (now operating as part of various local tour operators) and the Governor of Svalbard (Sysselmannen) are the key contacts. The Governor's office, based in Longyearbyen, handles permits for travel in protected areas — most of Svalbard's wilderness is national park and requires advance registration of routes. Maps at 1:100,000 scale, covering the whole archipelago, are sold locally and are essential for any off-road travel.