This paper is devoted to introducing an idea about coding and decoding theory. A compromise between tree codes and block codes, a hybrid tree-block code, is introduced. The concepts of discarding all improbable sequences in sequential decoding and decoding a whole block at a time in block decoding are used in this code. The structure of a hybrid tree-block code and its decoding scheme are discussed. The probability of error and the number of decoding operations are considered, and a comparison with block codes and tree codes are also considered.