Insertional mutagenesis is a method for identifying genes essential for a given biological process by using the integration of DNA as the mutagen, thereby facilitating the cloning of the mutated gene. The use of retrovirus‐mediated insertional mutagenesis in zebrafish has led to the mutation and rapid identification of hundreds of genes required for embryonic development and cell viability and growth, revealing the diversity of gene products required for the development of this vertebrate. Here, I will review the methodology of this approach and the results to date, as well as other potential ways to use insertional mutagenesis for genetic screens. Developmental Dynamics, 2003. © 2003 Wiley‐Liss, Inc.