Our original intention was for this chapter to be written by Sandra Handwerger (Rockefeller University, New York), but tragically she died in April 1996 before she could undertake the task. In our opinion, Sandra was one of the leading research workers on genetic aspects of glycopeptide resistance in enterococci. Although we never had the opportunity to meet her personally, her many publications on this subject have been and will continue to be a valuable source of both information and inspiration. This chapter has been based in part on the outline prepared by Sandra shortly before her death and is dedicated to her memory.