The development of powerful icebreakers and ice-strengthened cargo vessels has made winter navigation possible in the northern parts of the Baltic Sea as well as in some other seasonally, or even permanently, ice-covered sea areas. Thus the ice barriers, which previously closed these coasts and sea areas from shipping, have been mostly overcome. At a glance, the consequences of the current hazards of winter navigation seem to be limited to minor structural damage. No ice related ship disasters with large-scale consequences measurable in human or environmental losses have taken place in the Baltic Sea during the last decades. However, it should not be forgotten that some of the worst accidents in the history of shipping are closely related to ice. Titanic hit an iceberg in 1912 with the loss of life over 1500 persons. Exxon Valdez grounded in 1989 when trying to avoid ice on its route with the result of more than 40 000 tons of spilled oil. This kind of huge disasters have to be avoided in the Baltic Sea by careful risk management. On the other hand, the ability to counteract small but frequently occurring accidents, oil spills for instance, is important, too. In the Finnish-Swedish winter navigation system the risk of ice damage is traditionally controlled by the combined use of a) traffic regulation, which is mainly based on the extent of ice cover and the severity of the ice conditions, and b) ice class regulation and c) the icebreaker assistance based on the available fleet of state owned and operated icebreakers. Parallel, but to some extent different systems are in use in the other parts of the Baltic Sea.