We propose an interactive system that aims at lifting a 2D sketch into a 3D sketch with the help of existing models in shape collections. The key idea is to exploit part structure for shape retrieval and sketch reconstruction. We adopt sketch-based shape retrieval and develop a novel matching algorithm which considers structure in addition to traditional shape features. From a list of retrieved models, users select one to serve as a 3D proxy, providing abstract 3D information. Then our reconstruction method transforms the sketch into 3D geometry by back-projection, followed by an optimization ...