Starting in the late 1960s Shostakovich used twelve-tone rows in many of his most significant compositions. These rows usually occur melodically within individual vocal or instrumental parts and function as part of a larger musical fabric that does not otherwise involve twelve-tone technique. Though a number of previous scholars have addressed this phenomenon, some of its crucial aspects are thus far underexplored or even unacknowledged. After reviewing several basic characteristics of Shostakovich's twelve-tone usage, this article expands and refines our understanding of his twelve-tone melodies by situating them within the context of the broader concept of aggregate melodies. These melodies divide into four types, which are also relevant for music by other composers, and can be further described in terms of the relative tightness or looseness of their structural features. The article then reveals a fundamental trait prevalent in many of Shostakovich's aggregate melodies: they often convey distinct zones of chromatic activity, diatonic activity, or a mixture of both. Drawing on these terms and concepts, the final part of the article probes the second movement of the Twelfth String Quartet and the first movement of the Sonata for Violin and Piano, showing how we can relate Shostakovich's aggregate melodies to their musical surroundings in a deeper and more detailed way.