The present paper analyzes the use and understanding of the homology concept across different biological disciplines. It is argued that in its history, the homology concept underwent a sort of adaptive radiation. Once it migrated from comparative anatomy into new biological fields, the homology concept changed in accordance with the theoretical aims and interests of these disciplines. The paper gives a case study of the theoretical role that homology plays in comparative and evolutionary biology, in molecular biology, and in evolutionary developmental biology. It is shown that the concept or variant of homology preferred by a particular biological field is used to bring about items of biological knowledge that are characteristic for this field. A particular branch of biology uses its homology concept to pursue its specific theoretical goals. J. Exp. Zool. (Mol. Dev. Evol.) 299B:9–17, 2003. © 2003 Wiley-Liss, Inc.