Central Castries is small and easy to cover on foot. The market, the cathedral, Derek Walcott Square, and the harbour are all within a few hundred metres of each other.
For everywhere else, the workhorse is the minibus (locally called a "vouvarc" or just "the H bus" after their licence plate prefix). They run on fixed routes from the bus stations on Jeremie Street, are cheap (EC$2–8 a ride), and start before dawn. Get on, tell the driver where you are going, and pay when you get off. They generally stop running by about 8 p.m.
Taxis are everywhere but unmetered — agree the fare before getting in. Hire cars are useful for the rest of the island. Driving is on the left, the roads are winding and steep, and signage outside Castries is sparse.