Debit and credit are the two aspects of every financial transaction. Their use and implication is the fundamental concept in the double-entry bookkeeping system, in which every debit transaction must have a corresponding credit transaction(s) and vice versa.

Debits and credits are a system of notation used in bookkeeping to determine how to record any financial transaction. In financial accounting or bookkeeping, "Dr" (Debit) means left side of a ledger account and "Cr" (Credit) is the right side of a ledger account.

To determine whether one must debit or credit a specific account we use the modern accounting equation approach which consists of five accounting elements or rules. An alternative to this approach is to make use of the traditional three rules of accounting for: Real accounts, Personal accounts, and Nominal accounts to determine whether to debit or credit an account.

Debits and credits form two opposite aspects of every financial transaction. In basic terms, debit simply means left side, and credit means right side. To put this in context, the accounting equation, Assets = Liabilities + Equity (A = L + E), shows Assets on the left side of the equation, and Liabilities and Equity on the right side of the equation. Thus, for example, if an asset account increases, then one must also either decrease another asset account, or increase a liability account or equity account. For instance, from a bank customer's perspective, when a person deposits cash into his bank chequing account, this financial transaction has two aspects: the customer's cash-in-hand (the customer's asset) decreases and the customer's chequing account balance (the customer's asset) with the bank increases. The decrease in the cash-in-hand asset is the customer's credit while the increase in the asset balance in the bank chequing account is the customer's debit.