Building blocks are practical materials for playing, learning, and working at kindergartens, schools, universities, and companies. How did building blocks, which were primarily established as toys for children, come to be practical materials used in professional and educational settings? This study explores the historical implications of particular sets of building blocks in the interdisciplinary consolidation and transformation of techniques, materials, discourses, and subjects. By mapping the genealogy of building blocks from Froebel's gifts to their current systematization as interlocked blocks, this study proposes that building blocks should be understood not exclusively as concrete objects but as the materiality of a combinatorial program, which delineates a modular system characterized by a code of composition, context neutrality, and a semantic component.