High Quality Content by WIKIPEDIA articles! In coding theory, expander codes are a type of linear block code that arises by using bipartite expander graphs. Along with concatenated codes, expander codes are interesting since they can construct binary codes (codes using just 0 and 1) with constant positive rate and relative distance. Furthermore, expander codes can be both encoded and decoded in time proportional to the block length of the code. In fact, expander codes are the only known asymptotically good codes which can be both encoded and decoded from a constant fraction of errors in polynomial time.