In many industries like consulting or construction, highly qualified employees, i.e., experts or executive managers, have to be assigned to temporary projects. Obviously, the employees’ productivities in the respective projects are crucial for the employer’s optimal assignment decision, but assignment can also be affected by risk-incentive trade-offs. Moreover, taxation can alter the assignment decision, especially if employees are sent abroad as expatriates so that international tax law has to be taken into account. To address these issues simultaneously, we combine a human resource assignment problem with a principal–agent problem of the LEN type. Both wage taxation at the agents’ level and corporate taxation at the principal’s level are integrated. We show that national tax rules, the methods for avoiding double taxation, and the agents’ tax characteristics are important determinants of international assignment decisions. The effects of tax rate variations can be ambiguous and depend on whether the exemption method or the credit method are applied, in particular if agents make differing choices of residence. From a tax policy perspective, the exemption method should be preferred as the tax effects are more transparent and intuitive than under the credit method.