U.S. citizens typically require a visa to enter mainland China, and the length of stay in Chengdu is determined by the specific duration granted on that visa, which for most tourists is a 10-year multiple-entry visa allowing stays of up to 60 or 90 days per visit. However, Americans may visit Chengdu without a visa for up to 144 hours (6 days) under the 144-hour transit visa-free policy, provided they have a confirmed onward ticket to a third country or region (including Hong Kong or Macau) and remain within the designated administrative area. Additionally, U.S. citizens can stay in the island province of Hainan for up to 30 days visa-free for specific purposes like tourism or business, but this does not extend to Chengdu. For those just passing through, a 24-hour visa-free transit is available for all nationalities as long as they remain within the airport. It is essential for all travelers to register their residence with local police within 24 hours of arrival and ensure their passport is valid for at least six months.