A fundamental problem in biology is how structures form in the correct place in developing embryos. The development of the vertebrate limb is a wonderful system in which to study such pattern formation. My PhD project has focussed specifically on how anatomically distinct digits form at different positions along the anteroposterior axis of the limb. Sonic hedgehog is known to be pivotal in determining the number and pattern of digits, but little is known about genes that are expressed in response to Shh to encode anteroposterior positional values, and how these positional values are interpreted into digit anatomy. I have taken two approaches to identify genes that could be involved in determining digit identity in the limb; one in which I use Drosophila wing vein patterning as a model, and the other microarrays.