In Poland the road and rail network crosses many sensitive areas, such as national parks, landscape parks, wildlife reserves, landscape protection areas and Natura 2000 sites, i.e., the protected area system of the European Union, because of road density, high landscape diversity, and its mosaic pattern. As a consequence of Poland joining the European Union in 2004, many changes have happened and are still happening all over the country, especially in building new roads and railway lines. The harmonization of the Polish legal system with the EU directives required the improvement of environmental legislation making the monitoring before and after the building of such constructions necessary together with the preparation of environmental assessment studies. The animal migration problem has become one of the most important barriers in the decision-making process on where to build new roads and improve others. According to the previous plans, most of the roads that should have become expressways or highways of national or international importance also bring higher traffic and driving speed in those areas. As a consequence, the risk of collisions became higher and many motorists died in fatal accidents. On average, on the 160-km A2 highway running from Nowy Tomyśl to Konin, 40 accidents with mammals were recorded in one month in 2003. The consciousness of the society grew enormously following these events, and it also urged the appropriate governmental institutions, as well as private companies, investors, and non-governmental organizations, to study animals along the roads all over the country, with special attention to their movement. As a first step toward solving this problem, the identification of animal migration routes became an important task. Besides large species that can cause the death of the driver when colliding with a car (such as elk, deer, wild boar), several smaller animals (such as fox, badger, amphibians or reptiles) with vulnerable populations in the surveyed area were also studied, and the building of passages and bridges for wildlife has become not only an obligation but also a necessity both at the constructor as well as at the social level. Since 1997 more than ten overpasses and one underpass were built for large mammals (elk, deer, wolf, wild boar) in Poland. They are located along the E65 international road, Katowice - Kraków and the Przylesie - Nowogowczyce sections of the A4 highway, Poznan - Nowy Tomyśl and Nowy Tomyśl - Konin sections of the A2 highway, Stryszek- Białe Błota section of the no. 10. national road, and Komorniki - Stęszewo section of the no. 5. national road. The decision about the exact location of the game bridges and the game passage was made after detailed interviews with national park officials and foresters, in addition to the results of field work. The monitoring of the effectiveness of these constructions revealed a lot of mistakes and often proved no use of the mitigation measures by the target animals. The main reasons for non-functioning were too-small dimensions, especially width in all of game bridges; lack of screens separating the animals from noise; vibration, light and visual disturbances, no or not enough vegetation on the bridges; lack of guiding structures leading the animals to the passages; and lack of fences along the road. As a consequence of such results, mitigation measures were improved and maintained better. For small mammals, amphibians, and reptiles, nine underpasses were built in 2004 along the Budzisko - Augustów section of the international road called Via Baltica, Jeleniów section of the local road next to the E67 international road, and Chabówka - Rdzawka section of the E 47 expressway. The decision about where to put tunnels was made on the basis of field research (day and night transects, the sound monitoring of amphibians, and amphibian breeding sides investigations) made by national park staff, private companies, and volunteers. The follow-up monitoring of these structures showed that the effectiveness of the tunnels with guiding structures is nearly 100 percent for amphibians and reptiles and 85 percent for small mammals. In the following nine years (2005-2013) several more wildlife passages will be built on Polish roads along the Łódź - Częstochowa section of the A1 highway, Przylesie - Prądy section of the A4 highway, Rosnówek section of the no. 5. national road, Zywiec - Zwardoń section of the S69 international road, Wyszków - Skuszew section of the no. 8. national road, and Poznań - Kórnik section of the no. 11. national road. From among these constructions the most important passages will be along the Zywiec – Zwardoń section of the S69 international road, as they will be aimed to protect wildlife of international importance (bears, lynx, and wolves).