When do I need to register for an ABN?

In Plain English:

You need to register for an Australian Business Number (ABN) if you're running a business in Australia or making supplies connected with the indirect tax zone while carrying on an enterprise. Corporations Act companies are also entitled to have an ABN.

Detailed Explanation:

According to the A New Tax System (Australian Business Number) Act 1999, specifically section 8, you are entitled to an ABN if:

• You are carrying on an enterprise in Australia (subsection 8(1)(a)).
• In the course or furtherance of carrying on an enterprise, you make supplies that are connected with the indirect tax zone (subsection 8(1)(b)).
• You are a Corporations Act company (subsection 8(2)).

However, a limited registration entity (within the meaning of the A New Tax System (Goods and Services Tax) Act 1999) is not entitled to an ABN (subsection 8(3)).