On-line handwriting recognition systems are usually better than their off-line counterparts thanks to the accessibility to dynamic information such as stroke order, velocity, acceleration, and pressure. Whilst the exact value of velocity as well as acceleration or pressure is unlikely to be recoverable, the temporal order of the strokes or the pen trajectory is shown to be more promising for recovery. The experimental results reported in the literature suggest that the recovered pen trajectory actually improves the off-line recognition accuracy. This survey presents an overview and discussion of pen trajectory recovery methods developed to date.