Currently, 45 US states and the District of Columbia apply a sales tax, the scope of which is limited to domestic sales. In respect of crossborder transactions resulting in delivery of goods in the territory of the state, use tax should fill the void in the states' tax jurisdiction. However, that type of tax has proved to be ineffective. Since interstate commerce is the exclusive domain of the federal government, the states have no authority over out-of-state suppliers, unless they have sufficient physical presence (nexus) in the state. In order to persuade Congress to amend the physical presence rule and enable the states to require out-of-state sellers to collect use tax in respect of inter-state transactions, the states must drastically reduce the complexity of the obligation for sellers of having to account for use tax in different jurisdictions. In this article, the author describes the Streamlined Sales Tax Project, which is essentially aimed at harmonizing the states' sales and use taxes on a voluntary basis.