The provision regarding frontier workers in Art. 15 para. 4 of the tax treaty between Austria and Switzerland applies if two conditions are met: (1) the taxpayer’s residence and place of employment are close to the frontier, and (2) the taxpayer usually crosses the frontier every working day. This provision has recently been subject to a decision of the Austrian Administrative Supreme Court. The Court decided that the second condition is also met if – due to a secondment – the employment is exercised partly in Switzerland and partly in a third country. The Austrian resident is deemed to be a frontier worker in respect of his activity in Switzerland if during this period of time he fulfills the requirements of Art. 15 para. 4 of the tax treaty between Austria and Switzerland. Since in 2006 an amending protocol was signed and the provision in dispute was repealed, the decision will only be of minor importance for future cases related to Switzerland. However, Veronika Daurer analyses if the interpretation of the Administrative Supreme Court can be transferred to the other frontier workers provisions contained in Austria’s tax treaties with Germany, Italy, and Liechtenstein.