The rapid growth in the power of large‐scale computers has had a resolutionary effect on the study of charged‐particle accelerators that is similar to the impact of smaller computers on everyday life. Before an accelerator is built, it is now the absolute rule to simulate every component and subsystem by computer to establish modes of operation and tolerances. We will bypass the important and fruitful areas of control and operation and consider only application to design and diagnostic interpretation. Applications of computers can be divided into separate categories including: ▪ component design, ▪ system design, ▪ stability studies, ▪ cost optimization, and ▪ operating condition simulation.For the purposes of this report, we will choose a few examples taken from the above categories to illustrate the methods and we will discuss the significance of the work to the project, and also briefly discuss the accelerator project itself. The examples that will be discussed are: (1) the tracking analysis done for the main ring of the Superconducting Supercollider, which contributed to the analysis which ultimately resulted in changing the dipole coil diameter to 5 cm from the earlier design for a 4‐cm coil‐diameter dipole magnet; (2) the design of accelerator structures for electron‐positron linear colliders and circular colliding beam systems (B‐factories); (3) simulation of the wake fields from multibunch electron beams for linear colliders; and (4) particle‐in‐cell simulation of space‐charge dominated beams for an experimental linear induction accelerator for Heavy Ion Fusion.