The geometrical classification of the intercrystalline general type boundaries with various misorientations of contacting crystals and orientations of boundary planes was suggested previously. An arbitrary grain boundary breaks up into three families of thermodynamically stable boundaries as a result of fragmentation process due to annealing of polycrystalline sample. Geometrical representations of linear defects (dislocation, steps) and point defects (vacancy, interstitials) in intercrystalline and interphase general type boundaries of different families are developed. Representations about thermal excitations of boundary are developed. Different kinetic processes responsible for intercrystalline sliding, migration are considered, and expressions for characteristics of the low-temperature and high-temperature internal friction grain boundary peaks are obtained. Explanations of internal friction peaks observed near to the so-called ‘grain boundary peak’ are given. Mechanisms of atomic reorganization of grain boundary responsible for the grain boundary phase transitions are also considered. Conditions for the creation of amorphous atomic structure into boundary near to the fusion temperature of a crystal are specified.