This thesis proposes a new concept of form for Boris Blacher's Divertimento for Woodwinds, Duet for Flute and Piano, and Quintet for Flute, Oboe, Violin, Viola, and Violoncello. In 1950, Blacher began to use systematically varying metric units to provide logic to the apparently arbitrary rhythm of modern music. This practice led the few scholars who have studied his compositions to concentrate on the mathematical organization of metrical units, underestimating other musical elements. This dissertation is based on the idea that it is not the mere disposition of meters, but mostly the interaction between them and other musical elements that makes the peculiar durational scheme audible, thus perceptually relevant. Following this, the technique of expansion and contraction that becomes evident in the organization of the meters is also present in the disposition of durations at other hierarchical levels and in the pitch structure. Furthermore, the mathematical metrical scheme is the foundation for a deeper universe of systematic organization. Blacher's techniques provide a unique sense of movement to his compositions, the aural effect of an "elastically developing music." In Duet and Quintet, this idea is also applied in simultaneity to the registral disposition of pitches and textural development, suggesting vertical elasticity. As a result, Blacher's late compositions suggest a replacement of the traditional concepts of form and texture with a new idea of constantly moving, elastic shape. The methodological approach of this thesis is exclusively analytical and technical, with emphasis on durational and pitch organization, form, texture, and the interaction among these aspects. The individual and comparative analysis of the three compositions reveals a consistent conception of the musical space that emphasizes its bi-dimensional quality. In the Divertimento, the unitary conception of the vertical and horizontal construction is mainly reflected in the bi-dimensional treatment of interval classes that provides coherence to the motivic structure. In Duet and Quintet, this mere idea of consistent organization of the musical materials in the horizontal and vertical dimensions of the total space becomes a unique principle of formal definition, the elastic development of the musical content itself.