As an important part of the technology for human-machine interface

facial expression recognition(FER) have drawn much attention recently and numerous methods have been proposed.In this paper

we present the up to date development of this area in recent years.First

the three steps of the FER system are introduced: face detection

expressional feature extraction and expression classification.Second

the methods of feature extraction and expression classification are detailed in different categories.Then

we also introduce the facial expression databases which are widely used at present.Based on these databases

a comparison of the performances of several FER systems is presented.At last

we demonstrate the state of the FER technique and the possible challenges

and provide some advice about the current of FER development.