Understanding the interior ballistic characteristics of solid rocket motors is a daunting task for the motor designer because of the large number of coupled performance parameters. The performance parameters depend upon the internal ballistic properties of the motor, such as propellant burn rate. The designer has two basic options for developing new motors, built‐and‐test, or using a combination of numerical simulation, empiricalism, and small‐scale testing for validation, collectively known as virtual engineering. Virtual engineering, which requires appropriate models for the propellant, chamber, nozzle, and plume regions, is rapidly becoming the standard tool for designing new motors. We highlight some modern developments of physics‐based models used in virtual engineering, and comment on current trends.