Disclosed herein are a video decoding method and apparatus and a video encoding method and apparatus. In video encoding and decoding, multiple partition blocks are generated by splitting a target block. A prediction mode is derived for at least a part of the multiple partition blocks, among the multiple partition blocks, and prediction is performed on the multiple partition blocks based on the derived prediction mode. When prediction is performed on the partition blocks, information related to the target block may be used, and information related to an additional partition block, which is predicted prior to the partition block, may be used.