The objective of image fusion is to combine information from multiple images of the same scenc to accomplish tasks that cannot be achieved with a single image or source. Wavelets with their multiresolution property, have been proved to be effective in the integration of the coarse features and finer resolution details of these images to produce a well fused image. This paper surveys methods and principle of wavelet-based image fusion, pays attention to advantages of wavelet-based image fusion, and compares the characteristics of different image fusion rules. Furthermore, wavelet-packet-based, wavelet-frame-based and multiwavelet-based image fusion methods are presented.