Vouching is the act of reviewing documentary evidence to see if it properly supports entries made in the accounting records. For example, an auditor is engaged in vouching when examining a shipping document to see if it supports the amount of a sale recorded in the sales journal. Vouching can work in two directions. For example, an auditor can trace actual inventory items back to the accounting records to see if the items are properly documented, or start with the inventory records and trace back to the warehouse shelves to see if the inventory exists.

When engaged in vouching, an auditor is looking for any errors in the amount recorded in the accounting records, as well as ensuring that the transactions are recorded in the correct accounts. The auditor is also verifying that transactions have been properly authorized.

When vouching uncovers an error, the auditor may need to increase the sample size being audited in order to gain assurance that a system operates properly. An alternative is to engage in different auditing procedures.