A 3D model-based approach for the estimation of facial expressions from monocular video is presented. The deformable motion in the face is estimated using the optical flow constraint in a hierarchical analysis-by-synthesis framework. A generic face model parameterized by facial animation parameters according to the MPEG-4 standard constrains the motion in the video sequences. Additionally, illumination is estimated to robustly deal with illumination changes. The estimated expression parameters can be applied to other model to allow for expression cloning of face morphing.