Two interconnected challenges in C2 are to cope with uncertainty and to make timely deci-sions. From the standpoint of a commander these challenges may easily come into conflict with each other. Uncertainty, i.e. gaps in knowledge, may be reduced by collecting and processing additional information - but this takes time. To handle this dilemma the com-mander and his/her staff may have to make assumptions. An assumption is "a supposition on the current situation or a presupposition on the future course of events". If the assump-tions being made are invalid it may have negative consequences for the ability to reach the mission objectives. It is therefore important to assess and to follow up the assumptions during mission planning and execution, in order to make it possible for timely re-planning if necessary. However, even though the handling of assumptions is considered to be im-portant in both NATO´s planning directive COPD and in the Swedish counterpart SPL, nei-ther COPD nor SPL gives a clear guidance on how to assess the assumptions - apart from an exhortation to use a risk evaluation template. To date there is no theoretically grounded and systematically tested technique for assessing assumptions in C2. By using a design logic framework and techniques from the area of risk assessment this paper presents the initial step to a possible solution to these problems. The results are a design logic scheme and a design proposition for a technique that is potentially suitable for assessing assump-tions, to be tested in forthcoming empirical studies.