Illegal immigration across the external borders of the EU, outside border crossing points, reached record-breaking levels in 2015. Illegal immigration to Europe has proliferated and become less predictable over a period of five years. Even in Finland, the operating environment has been transformed in the last year from the perspective of immigration prevention and maintaining security. Illegal residence in Finland is forecast to increase. The years 2017–2020 will be crucial from the perspective of controlled residence in the country and the prevention of illegal immigration. In addition to Finland’s northern location, illegal immigration and residence in the country are probably less attractive because immigration control, the asylum process and the implementation of decisions on removal from the country, are known to be effective. In addition, there are no open shadow labour markets in Finland. These factors should help to prevent illegal immigration and residence in the country. However, individuals who have received a negative decision on their asylum applications are expected to form an entirely new group of people staying illegally in Finland. The consequences of this phenomenon will affect not only the Ministry of the Interior, but also the administrative branches of the Ministry of Social Affairs and Health, the Ministry of Economic Affairs and the Employment, the Ministry of Justice, the Ministry of the Environment and the Ministry for Foreign Affairs. The effects will also extend to municipalities and various organisations. The third Action Plan for the prevention of illegal immigration and residence focuses on the transforma- tion of the operating environment during 2015–2016, and the resulting challenges. The recommended measures recorded in the Action Plan will assist in maintaining internal security regardless of the drastic changes in the immigration situation. Key aspects of the Action Plan include ensuring the exchange of information between authorities, the effectiveness of decisions on removal from the country and enhanced immigration control inland, in a way that corresponds to the new situation. The Action Plan includes 25 proposed measures, whose implementation is assigned to various authorities. Success in preventing illegal immigration is monitored and coordinated by a cross-sectoral working group of public officials engaged in combating illegal immigration. The working group also monitors the practical implementation of the action plan by various authorities, and reports on the implementation of measures to the Ministerial working group on migration at least once a year. The National Bureau of Investigation has prepared a threat assessment type review of the status of illegal immigration as background for the Action Plan (Action Plan sections 4–4.6). The review outlines the situa- tion at national frontiers and at Europe's external borders in November 2016. The report also includes the viewpoints of the Ministry for Foreign Affairs, the Finnish Immigration Service and the Ministry of Social Affairs and Health on illegal entry and residence in the country.