Self-assembling peptides are members of a new class of molecules designed for tissue engineering and protein delivery. Upon injection in a physiological environment, self-assembling peptides form stable nanofiber hydrogels. Such biocompatible nanofibers can support three-dimensional growth and differentiation of many cell types. Self-assembling peptides are promising candidates for protein delivery, because they allow non-covalent binding of proteins, tethering of proteins, or incorporation of fusion proteins. Self-assembling peptides can be designed to deliver individual proteins or multiple factors, because the building blocks comprising self-assembling peptides can be designed with great flexibility.