A method for object modeling is presented and illustrated with examples. It extends to three dimensions a previously described technique for generating two-dimensional pictures using L-systems [Prusinkiewicz 1986]. The objects are modeled in two steps:

- A string of symbols µ is generated using an L-system
- µ is interpreted graphically as a sequence of commands controlling a turtle which maneuvers in three dimensions. The turtle can draw lines of various widths and colors, and trace boundaries of filled polygon.
Examples of synthesized objects are given and the construction of the corresponding L-systems is explained. Attention is focused on the modeling of plants. Stochastic L-systems are introduced to model various specimens of the same species. The turtle interpretation is extended to allow for incorporating predefined curved surfaces in the model. In spite of the apparent complexity of the resulting images, all discussed objects are generated by very concise L-systems.