Over the past two decades, developmental biologists have made great strides in understanding embryonic pattern formation at the genetic, molecular, and cellular levels. Much of this advancement can be attributed to the remarkable success of studies of pattern formation in model systems, such as the fruit fly Drosophila melanogaster. Identification of genes that play major roles in setting up the body plan, combined with the subsequent discovery that many of these genes are well conserved even between different phyla, has also led to a renaissance in the investigation of the links between evolution and development. Using information collected from studies of Drosophila development, my lab and others are beginning to explore the degree to which developmental pathways have been conserved or altered between various arthropods. Insights into the nature of developmental and molecular alterations will help us to understand the evolutionary changes in the mechanisms of pattern formation and provide a molecular basis for analyzing the diversification of body morphologies and developmental mechanisms.