RNA intereference and short-interfering RNA (siRNA) have been proven to be effective at decreasing the expression of target genes and provide a valuable tool for promoting and directing the growth of functional tissues for repair and reconstructive tissue engineering applications. siRNA is a gene-silencing mechanism that involves double-stranded RNA-mediated sequence-specific mRNA degradation and is a powerful mechanism for controlling cell behavior. The use of siRNA to reduce the expression of a target gene can induce the expression of one or more tissue-inductive factors, direct the differentiation of stem or progenitor cells, or remove a factor that inhibits regeneration, which can be useful in fundamental studies of tissue formation or in applications to promote in vivo regeneration. The potential of siRNA is illustrated through specific examples within the fields of angiogenesis, bone and nerve regeneration, and wound healing. In addition, challenges to deliver siRNA effectively for tissue engineering applications are addressed. siRNA represents a powerful tool to investigate and/or promote tissue formation, and numerous opportunities exist for identifying targets that promote regeneration of tissue and developing effective delivery systems.