Primitive shapes (see the section on Polygonal Modelling earlier in the module) are generated using a mathematical procedure and supplied parameter values.

Some modelling packages and 3D run-time systems support the definition of procedural models by the end-user. In practice, this means that it is possible to create scripts that can generate the geometry of an object when it is initialised.

While procedural modelling scripts can be very simple and draw simple well-defined shapes such as boxes, they can also be used to create complex organic shapes using genetic or fractal algorithms. This enables hugely complex geometries to be created efficiently.

Procedural modelling can be particularly effective for generating 'natural' geometry, e.g. landscapes, trees, fur, feathers, clouds, fire, and so forth, but also to generate models from data specifications (e.g. piping in a room) or to visualise data in an abstract manner ("information visualisation") on-the-fly.

For fractal algorithms, the most common method for 3D modelling is recursive subdivision, where a patchis recursively split up into pieces that are displaced by some irregular amount until some user defined limit is reached. The deeper the recursion goes the more complex (and more difficult to render in real time) the model becomes but by varying the parameters of the algorithm used it is possible to create models that offer complexity levels that are appropriate to the viewing distance.