The paper by Barton, Lien, and Lunde presents an engineering classification system for rock masses to design tunnel support. Analysis of 200 tunnel case records shows a correlation between the type and amount of permanent support and the rock mass quality Q. Q ranges from 0.001 (exceptionally poor rock) to 1000 (exceptionally good, unjointed rock). Q is determined by six parameters: RQD index, number of joint sets, joint roughness, joint alteration or filling, and two additional parameters for rock load and water inflow. These parameters represent rock block size, interblock shear strength, and active stress. The classification is illustrated with field examples and case records. Detailed analysis shows that suitable permanent support can be estimated for all rock qualities based on Q, support pressure, and excavation dimensions and purpose. Support pressure depends on Q, joint roughness, and joint set number, which determine rock mass dilatancy and freedom. Detailed recommendations include combinations of shotcrete, bolting, and cast concrete arches with appropriate spacing, length, and thickness. The boundary between self-supporting and supported tunnels can be determined by Q. Keywords: Classification, rock mass, joints, shear strength, tunnels, support pressure, shotcrete, bolts.The paper by Barton, Lien, and Lunde presents an engineering classification system for rock masses to design tunnel support. Analysis of 200 tunnel case records shows a correlation between the type and amount of permanent support and the rock mass quality Q. Q ranges from 0.001 (exceptionally poor rock) to 1000 (exceptionally good, unjointed rock). Q is determined by six parameters: RQD index, number of joint sets, joint roughness, joint alteration or filling, and two additional parameters for rock load and water inflow. These parameters represent rock block size, interblock shear strength, and active stress. The classification is illustrated with field examples and case records. Detailed analysis shows that suitable permanent support can be estimated for all rock qualities based on Q, support pressure, and excavation dimensions and purpose. Support pressure depends on Q, joint roughness, and joint set number, which determine rock mass dilatancy and freedom. Detailed recommendations include combinations of shotcrete, bolting, and cast concrete arches with appropriate spacing, length, and thickness. The boundary between self-supporting and supported tunnels can be determined by Q. Keywords: Classification, rock mass, joints, shear strength, tunnels, support pressure, shotcrete, bolts.