The fight against the illegal entry, residence and employment of foreigners is one of the key priorities of the immigration policies of the OECD countries. This irregular migration continues to persist, albeit at different levels for different receiving countries, both in countries that have expressed a political will to manage migration flows more effectively and to fight against the trafficking of labour, and in those that continue to receive a large number of immigrants every year as part of an active policy to recruit permanent migrant workers. In the light of the growing role of trafficking networks and their increasingly active involvement in moving labour across international boundaries, enhanced co-operation at both national and international levels is required to develop policies for preventing and combating the employment of foreigners in an irregular situation. In particular, whatever is done to combat the hiring of illegal immigrants must address the problem of undeclared work in general, and not just the employment of illegal immigrants per se. Better information on the risks and penalties involved in the use of illegal labour should also be directed at both employers and workers in industries where these illegal practices are prevalent, but also at employers that resort to the use of undeclared labour only on an occasional basis and at sending countries. Various specific measures adopted by a number of Member countries, such as the requirement to notify relevant government agencies prior to hiring, fiscal incentives for the employment of legal workers or the streamlining of hiring formalities, might be applied in a larger number of countries. The forging of partnerships between the relevant government agencies and employers’ and employees’ associations in each country should also be encouraged, together with the extension of international co-operation to control and manage immigration flows more effectively.