Decoders and methods for decoding polar codes and product codes The invention relates to a decoder (301) for decoding a polar code codeword, the polar code codeword resulting from encoding information data using a polar code encoding scheme. The polar code codeword comprises a plurality of code values. The decoder (301) comprises a processor (303) configured to select first successive code values to obtain a first sub-codeword and select second successive code values to obtain a second sub-codeword. The second successive code values follows the first successive code values. The processor is further configured to arrange the first sub-codeword and the second sub-codeword to form a product code matrix comprising a first matrix row with the first successive code values and a second matrix row with the second successive code values, a first matrix column comprising code values of the first sub-codeword and the second sub-codeword, and a second matrix column comprising code values of the first sub-codeword and the second sub-codeword. and decode the product code matrix using a product code decoding scheme to retrieve the information data from the polar codeword. The invention further relates to a decoder (311) for decoding a product code codeword.