Models of chemical structure play dual crucial roles in organic chemistry . First, they allow for the discovery and application of laws to the complex phenomena that chemists hope to understand. Second, they are a source of novel concepts that allow for the continuing development of structure theory and theoretical organic chemistry. In chemistry, therefore, the centrality and significance of models to the scientific enterprise is manifest and furthermore chemistry is a relatively clear, useful, and interesting context in which to consider more general philosophical questions about the nature and role of models in science.