Results of studies on animal models have shown that only guided periodontal tissue regeneration (GTR) will induce growth of new connective tissue fibers attached to new zement and bone tissue when the root surface had been exposed to plaque or pocket organisms. Studies of various authors suggest that it is exclusively the progenitor cells in the still existing periodontal ligament that permit regeneration. The development of GTR is based on biological principles. In the beginning its application was limited to periodontal surgery and has meanwhile expanded to include other areas such as implantology and oral surgery. Best results can be achieved in the periodontological treatment of three-walled bone defects and class II furcation involvements according to the data of several studies.