This year GPSS celebrates its 40th birthday. This paper reports on the development during these 40 years, starting with the first version developed by Gordon at IBM in 1961, and the following development of GPSS II, GPSS III, GPSS/360 and GPSS V, all IBM products. A major section is devoted to GPSS/H, which has dominated the GPSS scene during the last years. There is one section on the GPSSR family of GPSS versions and one on GPSS/PC and GPSS World. There are also many GPSS systems, projects and ideas of a mainly academic nature. A great number of GPSS textbooks are noted. The concluding section discusses the reasons for the popularity of GPSS.