The computational design of materials properties has been a long-term goal by a large segment of the theoretical and computational materials research community. One successful method for large-scale quantum-mechanical calculations is based upon the density-functional theory. In this talk I will review some of the breakthroughs that have lead to the widespread use of density functional theory for the design of materials. After doing so I will turn to applications of the density-functional theory to diamond chemical vapor deposition, fullerene-based materials, molecular magnets and light-harvesting molecules. Through a discussion of these applications I will show how density-functional-based methods can be used to understand and predict many properties of molecules. Such properties include binding and reaction energies, vibrational spectra, magnetic strength and ordering, growth mechanisms and polarizabilities. A discussion of possible future applications will be offered.