Disclosed herein are a video decoding method and apparatus and a video encoding method and apparatus. In video encoding and decoding, inter-prediction information for a target block may be derived, and inter prediction for a target block may be performed using the derived inter-prediction information. Combined inter-prediction information may be performed by combining multiple pieces of inter-prediction information, and the combined inter-prediction information may be added as a candidate to a list used for inter prediction. One of candidates in the list may be selected for inter prediction for the target block, and inter prediction using the selected candidate may be performed.