The Baltic Sea is one of the major maritime highway. During the middle ages, many of its southern ports belonged to the Hanseatic League. Since then, maritime traffic in the Baltic Sea has grown, having its trading activities internationalised through the diffusion of new shipping technologies. In 2007, the volume of cargo handled in Baltic ports was approximately 850 million tons. Moreover, the Baltic has an excellent network for passenger transportation: approximately 30 million people travel every year by ferry.
Nowadays, its winter traffic represents about one quarter of the annual traffic. Nevertheless winter navigation is relatively recent in the extremities of the gulfs of Bothnia and Finland. Indeed, at the beginning of maritime transportation, the activity was seasonal and occurred only in open water, threatening to stop completely in winter due to sea ice formation. But for over a century, the evolution of materials and shipping techniques has allowed continuous maritime navigation. Despite the fact that sea ice conditions require the assistance of icebreakers, adapted port infrastructures, the introduction of ice classes and winter restrictions to the navigation, harsh winter conditions inevitably induce an increase in maritime incidents. There is the question of the future of winter navigation in the context of global warming and a possible significant reduction of sea ice.