Stamp duty is generally imposed on 'instruments' (documents) rather than transactions. It is a complex area of law and is not dealt with at length here. Many types of agreement cannot be enforced unless they are put into writing and stamp duty is paid, for example, the transfer of real estate and mortgage documents. Duty is also payable on applications to transfer the registration of a motor vehicle. Deeds or transfers of any kind not otherwise specified in the Second Schedule of the Stamp Duties Act 1923 are chargeable with nominal duty. Where the stamp duty is not a flat rate, but is paid on a percentage of some amount, it is known as 'ad valorem' (according to the value) duty.

The rates of duty vary according to the type of transaction. Although the rate of duty is often low (ranging from $1 per $100 of value to $5.00 per $100 of value), the total charge can be considerable, depending on the value of the property transferred. Concessional rates are available for people buying a first home.

When either an interest in a shared principal place of residence, or registration of a motor vehicle is transferred between spouses, there is no stamp duty payable; an exemption is also available to people who have lived in a domestic partnership (see the Family Relationships Act 1975) for more than three years, or a total of three of the last four years, or who have a child together.

In order to have the stamp duty waived on the transfer of the shared home or motor vehicle following separation, it is necessary to complete a special statutory declaration (available from Revenue SA), or obtain a court order for the division of the property.