Through large-scale efforts like the human genome project vast amounts of biological sequence data have become available. However, the interpretation of this data lags far behind its production. In order to make sense of biological sequence data computational tools are crucial. We will study the comparison of biological sequences as an example. We will see how methods and well-established results from statistical physics can be applied to improve computational biology tools. On the other hand, we will find that computational biology provides problems which give new insights into the statistical physics of disordered systems.