This report deals with the problem of uncertainty in connection with long range planning. Key issues are: Is it possible to strengthen the ability of an organization to cope with the unexpected? How could one plan in face of the (partly) unknown? The report is based on experience of Swedish defence analysis, mainly from the field of civil preparedness planning. Four cases from Swedish defence planning are included. The aim of the report is to develop a conceptual framework and formulate a set of principles useful for long range societal planning. Many long range planning problems in civil preparedness necessarily deal with judgements on technical development, domestic social trends, trends in international interdependence, global and regional geostrategic changes, and objectives and motives of a potential aggressor. These factors are all essentially uncertain. Therefore, it is important that preparedness measures not be based on specific assumptions of one or two scenarios. Rather, measures should be chosen which are likely to be effective under a wide range of possibilities. One conclusion is that it is necessary to accept a certain amount of uncertainty as inevitable. Shifting focus from what we know or believe to be true to what we cannot know, we will look for other solutions. Creating action space for the future becomes an important concern - to successively take decisions and to develop the ability to act on unexpected situations as they emerge. This ability could be developed through games and exercises. Another conclusion is that uncertainties relevant to a decision situation should be made explicit and understandable to the decision makers. When many factors are uncertain, a simple systems model is often preferable to a more complex one. A simple model enables the decision maker to comprehend the lines of argument which underlie the decisions and hence to adequately judge the effects of uncertainty.