What is the difference between an ACN and an ABN?
An ACN is your Australian Company Number, issued by ASIC the moment the company is registered — it identifies the legal entity. An ABN is your Australian Business Number, issued by the ATO, and it is what you use to trade, invoice, and register for GST. A company gets an ACN first and then applies for an ABN, which incorporates the ACN digits. Sole traders have an ABN but no ACN, because there is no company.