A gateway is any person or organization that allows users to deposit money into or withdraw money from the Ripple liquidity pool. The gateway accepts currency deposits from users and issues balances in the Ripple distributed ledger. Additionally, gateways redeem currency balances according to the ledger they hold when the currency is withdrawn. In practice, gateways are similar to banks, but they are connected by one global ledger known as the Ripple protocol. Depending on the type and degree of user interaction with the gateway, the gateway may have anti-money laundering (AML) or know your customer (KYC) policies that require verification of identification, address, nationality, etc., to prevent criminal activity. Popular gateways as of 2017 include: Bitstamp, Gatehub, Ripple Fox, Tokyo JPY, Mr. Ripple, RippleChina, and The Rock Trading.
Trustlines and Rippling
Users must "extend trust" to the Ripple gateway holding their deposit. This guide to creating a trustline procedure shows the Ripple network that the user is comfortable with the counterparty risk of the gateway. Additionally, the user must enter a quantitative limit on this trust and create similar limits for each currency deposited in this gateway.