The present disclosure provides a decoding method and apparatus, an encoding method and apparatus, and a device. The decoding method includes: determining prediction-mode flag information of a current block, the prediction-mode flag information includes a flag value of each of one or more of N candidate prediction modes; when the flag value is a first value, the flag value indicates that a candidate prediction mode is enabled, and when the flag value is a second value, the flag value indicates that the candidate prediction mode is disabled, and for the flag value of one of the N candidate prediction modes, if the current block does not satisfy a decoding condition of the flag value of the candidate prediction mode, the flag value is a derived flag value of the candidate prediction mode; determining a target prediction mode used by the current block according to the prediction-mode flag information, where the target prediction mode is one of the N candidate prediction modes; and decoding the current block according to the target prediction mode. The present disclosure can improve the encoding performance.