In this paper, we present an intuitive interface for interactively posing 3D facial expressions. The user can create and edit facial expressions by drawing freeform strokes, or by directly dragging facial points in 2D screen space. Designing such an interface for face modeling and editing is challenging because many unnatural facial expressions might be consistent with the ambiguous user input. The system automatically learns a model prior from a prerecorded facial expression database and uses it to remove the ambiguity. We formulate the problem in a maximum a posteriori (MAP) framework by combining the prior with user-defined constraints. Maximizing the posterior allows us to generate an optimal and natural facial expression that satisfies the user-defined constraints. Our system is interactive; it is also simple and easy to use. A first-time user can learn to use the system and start creating a variety of natural face models within minutes. We evaluate the performance of our approach with cross validation tests, and by comparing with alternative techniques.