US subnational state tax regimes operate independently of - and often differently from - the US national tax regime. These differences can have important international implications, such as the use of formulary apportionment rather than arm's length separate accounting for attributing a multinational corporation's income to a taxing jurisdiction. This article examines three recent developments in US state taxation that raise issues of international interest: (1) state court decisions sustaining corporate income tax jurisdiction over taxpayers without a permanent establishment or other physical presence in the state; (2) a state court decision limiting the dividends-received deduction for foreign subsidiaries to foreign subsidiaries that earn taxable income in the state, despite other state court decisions suggesting that such a provision is unconstitutionally discriminatory; and (3) the continuing evolution of the Streamlined Sales and Use Tax Agreement offering vendors simplified tax administration and relief from audit exposure in return for collecting taxes in all the states that have complied with the Agreement. Because the US Supreme Court has declined to intervene in the first two controversies, and the third remains a work in progress, these developments remain matters of concern for the international business community.