The structure of Ge 20 Te 80 , Ge 15 Cu 8 Te 77 and Ge 15 Cu 5 Te 80 glasses was investigated by diffraction techniques and extended X-ray absorption fine structure measurements. Large structural models were generated by fitting experimental data by the reverse Monte Carlo simulation technique. In Ge 20 Te 80 glass, both Ge and Te obey the 8−N rule, and the structure is built up of GeTe 4 tetrahedra connected via Te–Te bonding or shared Te atoms connected to two Ge atoms. The coordination number of Te is significantly higher than 2 in Ge 15 Cu 8 Te 77 . The average coordination number of Cu is 3.41±1 in this alloy. In Ge 15 Cu 5 Te 80 glass, Cu binds mostly to Te, while Cu–Cu bonding is significant in Ge 15 Cu 8 Te 77 .