An encoding method and apparatus and a decoding method and apparatus are provided. The decoding method includes extracting a down-mix signal and spatial information regarding a plurality of channels from an input bitstream, and generating a three-dimensional (3D) down-mix signal by performing a 3D rendering operation on the down-mix signal using the spatial information and a filter, wherein the sum of the number of valid signals of the down-mix signal, the number of valid signals of the spatial information, and the number of valid signals of co-efficients of the filter is less than the number of valid signals of the 3D down-mix signal. Accordingly, it is possible to efficiently encode multi-channel signals with 3D effects and to adaptively restore and reproduce audio signals with optimum sound quality according to the characteristics of an audio reproduction environment.