Brahms had already composed over 20 string quartets (he confessed to a friend that he had burnt all of that "stuff") before he finally presented his Opus 51 to the public. In the end only three surviving works managed to withstand his high self-criticism. We are now publishing the two passionate dark Quartets op. 51 separately from the rather more lively Opus 67, about which a reviewer of the time wrote, "This time Brahms seems to have taken it upon himself to walk along a sunny path through a meadow". The basis for this edition is the volume in the New Complete Edition of Brahms' works, published in 2004 by Henle, for which previously missing sources in a Swiss bequest were consulted for the first time.