The objective of this research is to create a process for the design and fabrication of structural components with optimized composite microstructures. Here the term "microstructure" refers to the component's inner structure, the scale of which is small compared to the scale of the component; the microstructure is not, for examples relevant to this project, microscopic. The major phases of the research program include: (1) creating a multi-scale design process to optimize a component and its microstructure, <br/>(the microstructure's geometry will be a lattice or, for composites with multiple constituent materials, a set of intertwined lattices and the iterative design process will address material density, anisotropy, and orientation in distinct steps, identifying optimal rotations and distortions for the lattice to create an optimized microstructure), (2) refining and extending hybrid fabrication techniques, based on Solid Freeform Fabrication, to construct the components with finely scaled microstructures, and (3) designing, fabrication and testing example components. <br/><br/>If successful, this research will lead to practical procedures for the design and fabrication of lightweight, high performance structure and machine parts. The ability to design the microstructure within a component will provide the opportunity to adjust material properties where appropriate, and to adjust the properties via gradients rather than discontinuities. Applying this concept to composites made from multiple constituent materials, one could design a component that has two different material properties, for example, stiffness and thermal or electrical conductivity, optimized independently.