The physical mechanism behind the bootstrap current is explained, and theconsequences are discussed with the emphasis on the two main objectives offusion plasma, confinement and MHD stability. For a tokamak reactor that isoptimized for good confinement and stability, and that has a limited size, thetotal plasma current exceeds the bootstrap current by a factor of three tofive and therefore almost all the plasma current must be driven through othermeans. Furthermore, the neoclassical tearing mode which is driven by thebootstrap current is expected to be the limiting MHD instability in thesereactors. Raising the fraction of the bootstrap current is not expected to bebeneficial for confinement and stability expect when broad pressure profiles(internal transport barriers) can be realized. In stellarators severaloptimizations are possible, either optimizing the current to zero such that itdoes not destroy the desired topology, and it does not generate anycurrent-driven instabilities, or using the current to generate some of thepoloidal field.