This chapter examines the integration of living materials into architectural design, focusing on the use of mycelium composites formed through fungal biotransformation. As architecture faces increasing demands for environmental responsibility, material innovation has turned toward biological systems capable of replacing high-impact construction materials. Mycelium, the filamentous body of fungi, offers a biologically active and biodegradable alternative. When cultivated on lignocellulosic waste substrates, it produces composites that are lightweight, renewable, and suitable for a wide range of applications. The chapter provides an overview of the historical development, material behavior, and fabrication strategies associated with mycelium-based construction. It highlights how advances in additive manufacturing have enabled complex forms that support both fungal viability and architectural function. By combining digital design with microbial growth, new techniques allow for the creation of geometries that optimize aeration, structural performance, and environmental interaction. Central to the discussion is the concept of transcalar design: Biological processes at the molecular and cellular level are shown to influence, and be influenced by, decisions at the component and building scale. Computational tools support this multi-scalar coordination by enabling responsive geometries and adaptive material behavior. The chapter argues for a shift in architectural thinking toward systems that incorporate growth, decay, and regeneration as intrinsic design parameters. By rethinking materiality through the lens of living systems, the chapter proposes a framework for sustainable construction rooted in biological intelligence. This approach challenges traditional notions of permanence and uniformity, offering new possibilities for ecological integration and design agency.