Abstract: We present "JustDrawIt", a sketch-based system for creating 3D curves suitable for surfacing. The user can sketch in a free-form manner from any view at any time, and the system infers how those sketch strokes should be added to the drawing. Specifically, existing curves are projected to 2D and analyzed to see if the stroke edits or extends an existing curve, or if the stroke should make a new curve. In the former case the 2D stroke is promoted to 3D using the position of the existing curve, and then joined to that curve. In the latter case, we use additional spatial information (e.g. temporary 3D surfaces) to create a new curve in 3D. All non-sketching interactions are based on unintrusive context-aware, in-screen pie menus designed for rapid pen-based input. We also provide novel rendering styles and aides for interpreting and working with 3D sketches. Finally, we support snapping together curve networks and specifying normals in order to create surface models.