Many of the methodologies within the Lean Start-up and Innovation movements rely on formulating hypotheses or assumptions on which your solution/idea relies. Once available, those are structured as business experiments and fed into the customer validation process. We have found that to be a big challenge for many individuals and teams. Firstly, because formulating proper hypotheses and surfacing assumptions is not simple. Second, because of our general tendency to work with full constructs rather than identifying fundamental assumptions. We have developed the Assumption Canvas as a structured way of questioning that helps us in the hypothesis building process.