Activin is a member of the transforming growth factor beta family of growth and differentiation factors. Initially discovered as a protein that stimulates release of follicle-stimulating hormone, it is now well accepted as an important regulator of cell growth and differentiation. Most interestingly, a series of previous studies have revealed novel roles of activin in inflammation and repair. Our own results have provided evidence for an important function of activin in cutaneous wound repair as well as in neuroprotection, and these data will be summarized and discussed in this chapter.