What is the difference between IAS and BAS?

In Australia, Business Activity Statements (BAS) and Instalment Activity Statements (IAS) are forms lodged by businesses to the Australian Tax Office (ATO) to declare tax owing to the ATO.

Simply, the difference between BAS and IAS is that IAS does not show payments owing to or by the ATO for general service taxes (GST) because the enterprise submitting the IAS is not registered for GST.