A cashier's check (or cashier's cheque, cashier's order) is a check guaranteed by a bank, drawn on the bank's own funds and signed by a cashier. Cashier's checks are treated as guaranteed funds because the bank, rather than the purchaser, is responsible for paying the amount. They are commonly required for real estate and brokerage transactions.

Genuine cashier's checks deposited into a bank account are usually cleared the next day. The customer can request "next-day availability" when depositing a cashier's check in person. Forged cashier's checks may bounce 2 weeks after being deposited.

When cashier’s checks took weeks to clear the banks, they were often forged in fraud schemes. The recipient of the check would deposit it in their account and withdraw funds under next-day availability, assuming it was legitimate. The bank might not be informed the check was fraudulent until, perhaps, weeks after the customer had withdrawn funds made available by the fraudulent deposit, by which time the customer would be legally liable for the cash already withdrawn.

A customer asks a bank for a cashier's check, and the bank debits the amount from the customer's account immediately and assumes the responsibility for covering the cashier's check. That is in contrast with a personal check, for which the bank does not debit the amount from the customer's account until the check is deposited or cashed by the recipient.

A cashier's check is not the same as a teller's check, also known as a banker's draft, which is a check provided to a customer of a bank or acquired from a bank for remittance purposes and drawn by the bank, and drawn on another bank or payable through or at a bank.

A cashier's check is also different from a certified check, which is a personal check written by the customer and drawn on the customer's account, on which the bank certifies that the signature is genuine and that the customer has sufficient funds in the account to cover the check.

Also, a cashier's check should not be confused with a counter check, which is a non-personalized check provided by the bank for the convenience of a customer making withdrawals or payments, but it is not guaranteed and is functionally equivalent to a personal check.