Methods and apparatuses for invoice numbering are disclosed. In one embodiment, the method comprises A method for electronically generating invoices for a party with invoice numbers where there are no gaps between invoice numbers nor duplicate invoice numbers, the method comprising: receiving, at a database, a first request to prepare an invoice for the party; preparing the invoice, including calling a command to assign an invoice number to the invoice; acquiring a limited-time lock to cause any other requests to the database related to obtaining invoice numbers for invoices for the party to wait until the invoice number has been assigned and persisting the invoice to the database has completed; assigning the invoice number for the invoice after confirming a highest invoice number already stored in the database, where the invoice number is assigned the number that is next sequentially to the highest invoice number; after assigning a number to the invoice, then persisting the invoice with the assigned invoice number to the database; and releasing the lock in response to completely persisting the invoice with the assigned invoice number to the database.