This tutorial will cover the various aspects of medium (1-52 kV), high (>52 kV) gas-insulated substations (GIS) and gas-insulated transmission lines (GIL) in technical performance, economic evaluation, advantages in environmental impact, substations and personal safety. The technical features of switching capabilities and ratings, reliability, space requirements, monitoring, installation procedures, commissioning, operation, maintenance and recycling after and of life time. The theoretical basis of GIS and GIL technology will be explained on practical examples. The design, manufacturing and testing process in the factory will be covered and in a wide view of executed applications overview will be given in which cases GIS and GIL have been chosen. Interfaces to connect GIS and GIL in substations with other equipment as overhead line, transformer or cables will be explained and a view into life cycle cost analysis will be given.