Cayenne–Félix Eboué Airport is 17 km southwest of the city, at Matoury. Air France and Air Caraïbes run daily long-haul flights from Paris-Orly; regional flights connect to the French Caribbean (Martinique, Guadeloupe), Belém, Paramaribo and a few other Latin American capitals. There are no direct flights from the rest of Europe or from North America — most travellers connect via Paris or the French Antilles.
Overland is possible but slow: from Suriname, take a shared taxi from Paramaribo to the Maroni river at Albina/Saint-Laurent-du-Maroni, cross by pirogue, and continue by bus or shared car to Cayenne (about six hours total once you've cleared the border). From Brazil, the road crosses the Oyapock at Saint-Georges and runs four hours up to Cayenne on a sealed road. Bring your passport: French Guiana is officially France and Schengen rules apply.