The number is usually printed in three groups of three digits, and preceded by the letters ACN must be quoted on all correspondence and invoices issued by the company.
[1] The Australian Company Number (ACN) was adopted in Australia on 1 July 2000, as one of the complementary measures when the Goods and Services Tax (GST) was introduced.
An ACN is not required on (at least): packaging and labelling, including envelopes and transport documents; advertisements which do not make a specific offer which is capable of being accepted (such as advertisements which only promote the company and its goods or services in general); credit cards and credit card vouchers; machine-generated receipts, including cash-register receipts; business cards and 'with compliments' slips; and items which are not documents (e.g., vehicles, television advertisements).
Other measures introduced with the introduction of the GST included the Australian Business Number (ABN), removal of wholesale sales tax exemptions and changes to the FBT and changes to the treatment of trusts and charities.
Prior to the introduction of the nine-digit ACN, filings with ASIC were based on the company name, which might vary from one to 80 characters.