From Phnom Penh: Buses run roughly every hour from the Phnom Penh central bus station. The journey takes three to four hours depending on the operator and traffic. Giant Ibis and Mekong Express are reliable choices; book online the day before. The fare is $7–12. A taxi (booked through a guesthouse or app) costs around $35 and takes about 2.5 hours. No train service operates.
From Sihanoukville: The coast road between Sihanoukville and Kampot is about 110 kilometres. Minibuses run several times daily in about two hours; regular bus services also exist.
From Bangkok: Combination bus-and-taxi services run from Bangkok's Southern Bus Terminal directly to Kampot via the border at Hat Lek/Cham Yeam. The journey takes approximately nine hours. Many travellers cross at Koh Kong and continue by minibus, but the direct route is easier.