Book of original entry is another name for a journal, the accounting record where a business transaction is recorded for the very first time, in the order it occurs, before it is later posted to the appropriate accounts in the general ledger. The name reflects exactly what the record does: it captures each transaction at its origin, in chronological order, as the foundation for everything that follows in the accounting process.
Why the first record matters
Before a transaction's effects can be reflected in individual accounts such as Cash, Accounts Receivable, or Sales, it has to be analyzed to determine which accounts are affected and by how much, following the double-entry rule that every entry's total debits must equal its total credits. The book of original entry is where that analysis is first documented, with the date, the accounts and amounts involved, and a brief description of the transaction, before the entry is transferred, or posted, into each affected account.
General versus special journals
Smaller businesses, or specific unusual transactions, may use a single general journal as the book of original entry for everything. Businesses with high transaction volume typically use several special journals instead, each dedicated to one recurring transaction type — a sales journal, a cash receipts journal, a cash disbursements journal, and a purchases journal are common examples — which lets routine, repetitive entries be recorded far more efficiently than writing out a full general journal entry for every single transaction.
How the term has evolved with technology
In a fully computerized accounting system, the concept still exists even though a human bookkeeper rarely manually writes journal entries for routine transactions anymore; the software automatically creates the appropriate journal entry the moment an invoice is generated, a payment is received, or a bill is entered, with the underlying logic of recording the transaction first, before posting it to the ledger, unchanged from the manual bookkeeping era.
Why the distinction from the ledger still matters
Keeping the book of original entry conceptually separate from the general ledger preserves an auditable, chronological trail of every transaction exactly as it was first recorded, which auditors and investigators rely on when tracing a specific ledger balance back to the original transactions that produced it, a process that would be far harder if transactions were posted directly into ledger accounts with no intermediate journal record at all.
A simple worked example
When a company sells $2,000 of merchandise on credit, the transaction is first recorded in the sales journal, the book of original entry for credit sales, with a debit to accounts receivable and a credit to sales. Only afterward is that same entry posted into the individual Accounts Receivable and Sales accounts within the general ledger, preserving a clear, chronological record of the original transaction separate from the ledger balances it eventually updates.