Brahms had already composed more than twenty string quartets (he will admit to a friend having burned all these “tricks”) before daring to present his opus 51 to the public. From this work, only three works remained, having escaped to the composer's self-censorship - numerous correction strata testify to the commitment to the smallest detail. We publish the two op. 51, passionate and somber, separated from an op. 67 rather playful. Our edition is based on the volume of the new complete edition of the works of Brahms, volume for which, for the first time, the edition was able to draw on sources, hitherto extinct, coming from a Swiss legacy.