A credit card is part of a system of payments named after the small plastic card issued to users of the system. It is a card entitling its holder to buy goods and services based on the holder's promise to pay for these goods and services. The issuer of the card grants a line of credit to the consumer (or the user) from which the user can borrow money for payment to a merchant or as a cash advance to the user.
Credit cards are issued after an account has been approved by the credit provider, after which cardholders can use it to make purchases at merchants accepting that card.
When a purchase is made, the credit card user agrees to pay the card issuer. The cardholder indicates consent to pay by signing a receipt with a record of the card details and indicating the amount to be paid or by entering a personal identification number (PIN). Also, many merchants now accept verbal authorizations via telephone and electronic authorization using the Internet, known as a 'Card/Cardholder Not Present' (CNP) transaction.
Electronic verification systems allow merchants to verify that the card is valid and the credit card customer has sufficient credit to cover the purchase in a few seconds, allowing the verification to happen at time of purchase. The verification is performed using a credit card payment terminal or Point of Sale (POS) system with a communications link to the merchant's acquiring bank. Data from the card is obtained from a magnetic stripe or chip on the card; the latter system is in the United Kingdom and Ireland commonly known as Chip and PIN, but is more technically an EMV card.
Other variations of verification systems are used by eCommerce merchants to determine if the user's account is valid and able to accept the charge. These will typically involve the cardholder providing additional information, such as the security code printed on the back of the card, or the address of the cardholder.
Each month, the credit card user is sent a statement indicating the purchases undertaken with the card, any outstanding fees, and the total amount owed. After receiving the statement, the cardholder may dispute any charges that he or she thinks are incorrect (see Fair Credit Billing Act for details of the US regulations). Otherwise, the cardholder must pay a defined minimum proportion of the bill by a due date, or may choose to pay a higher amount up to the entire amount owed. The credit provider charges interest on the amount owed if the balance is not paid in full (typically at a much higher rate than most other forms of debt). Some financial institutions can arrange for automatic payments to be deducted from the user's bank accounts, thus avoiding late payment altogether as long as the cardholder has sufficient funds.
信用卡是壹種非現金交易付款的方式（參見信用卡交易），是簡單的信貸服務。信用卡壹般是長85.60毫米、寬53.98毫米、厚1毫米的塑料卡片（尺寸大小是由ISO 7810、7816系列的文件定義），由銀行或信用卡公司依照用戶的信用度與財力發給持卡人，持卡人持信用卡消費時無須支付現金，待賬單日時再進行還款。除部份與金融卡結合的信用卡外，壹般的信用卡與借記卡、提款卡不同，信用卡不會由用戶的帳戶直接扣除資金。
申請
多數情況下，具有完全民事行為能力（中國大陸地區為年滿18周歲的公民）的、有壹定直接經濟來源的公民，或沒有直接經濟來源的在校大學生（僅限本科生，部分銀行更限於中國“211工程”之重點大學），可以向發卡行申請信用卡。有時，法人也可以作為申請人。申請方式壹般是通過填寫信用卡申請表，並提交壹定的證件復印件與證明等給發卡行。申請表都附帶有使用信用卡的合同，申請人授權發卡行或相關部門調查其相關信息，以及提交信息真實性的聲明，發卡行的隱私保護政策等，並要有申請人的親筆簽名。
核發
通常，銀行會根據申請資料，考察申請人多方面的資料與經濟情況，以及各銀行內部的信審政策之標準，來判斷是否發信用卡給申請人。考慮的因素有，申請人過去的信用記錄、申請人已知的資產、職業特性等。發卡行審核的具體因素與過程屬於商業機密，外界壹般很難了解。各個發卡行的標準也不盡相同，因此，同樣的材料在不同的銀行可能會出現核發的信用額度不同，信用卡的種類不同，甚至會出現有的銀行審核通過，而有的銀行拒發的情況
開卡
由於信用卡申請通過後是通過郵寄將卡片寄出等方式，所以並不能保證領取人就是申請人。為了使申請人和銀行免遭盜刷損失，信用卡在正式啟用前設置了開卡程序。開卡主要是通過電話或者網絡等，核對申請時提供的相關個人信息，符合後即完成開卡程序。此時申請人變為卡片持有人，在卡片背後簽名後可以正式開始使用。