0. Introduction -- 0.1 The Structure of the Simulator GPSS-FORTRAN Version 3 -- 0.2 Modelling -- 0.3 Ease of Use -- 0.4 Acknowledgements -- 1. The Flow Control -- 1.1 Model Classification -- 1.2 State Transitions -- 1.3 The Subroutine FLOWC -- 1.4 Simultaneous Activities -- 2. The Simulation of Continuous Systems -- 2.1 Differential Equations in GPSS-FORTRAN Version 3 -- 2.2 Scheduled State Transitions -- 2.3 Conditional State Transitions -- 2.4 The Subroutine EQUAT -- 2.5 Adding to or Removing from a Chain Using TCHAIN andNCHAIN -- 2.6 Integration Methods -- 3. Queued Models -- 3.1 Transactions -- 3.2 Subroutines for Processing Transactions -- 3.3 An Example of a Model -- 4. Stations and Queued Models -- 4.1 Facilities -- 4.2 Multifacilities -- 4.3 Pools and Storages -- 4.4 Coordination in Processing Paths -- 4.5 Families -- 4.6 Match Stations -- 5. Evaluation and Representation of the Results -- 5.1 The Behaviour of the Queues -- 5.2 The Computation of Frequency Tables -- 5.3 Output of the State of the Model -- 5.4 Auxiliary Aids -- 6. The Generation of Random Numbers -- 6.1 Generators of Random Numbers -- 6.2 Generation of Uniformly Distributed Random Numbers -- 6.3 Generation of Random Numbers with an Arbitrary Distribution -- 6.4 Random Numbers in GPSS-FORTRAN Version 3 -- 7. Input and Output -- 7.1 Free Format Input -- 7.2 Output of Plots -- 7.3 Output of Bar Charts Using GRAPH -- 7.4 Operational Modes -- 7.5 Graphic Representation -- References.