If you want to base a new drawing on an existing piece of artwork, you can trace it. For example, you can create a graphic based on a pencil sketch drawn on paper. Or, import a raster image saved in another graphics program, and trace over it.
The easiest way to trace artwork is to open or place a file into Illustrator, and automatically trace the artwork with the Image Trace command.
Several tracing presets provide pre-specified tracing options for specific types of artwork. For example, if you’re tracing an image that you plan to use as a technical drawing, choose the Technical Drawing preset. All the tracing options change for optimal tracing of a technical drawing.
You can also control the level of detail and how the tracing is filled, and even save the settings as a custom preset for future use.
For a video on tracing, see Image Trace in Illustrator CS6 on Adobe TV.
For users of Illustrator CS5 and earlier versions: Use the Live Trace feature to trace an image into vector artwork. See Using Live Trace.