INTRODUCTIONCtenophores, or comb jellies, are a group of marine animals whose unique biological features and phylogenetic placement make them a key taxon for understanding animal evolution. Some characteristics are present in nearly all ctenophores, including biradial symmetry, comb rows composed of linked cilia, an apical sensory organ, and two tentacles bearing specialized adhesive cells. All ctenophores studied thus far have the same stereotyped cleavage program and go through a specific stage of development known as the cydippid larva, after which adult structures develop and diverge greatly among species; this is particularly useful for comparative studies. In some cases, gene expression patterns appear to be conserved. Of particular interest is the finding that some genes are expressed in regions of the ctenophore body that are not morphologically distinct from the adjacent areas. However, it has proven difficult to determine the orthology of some genes, possibly because of the extreme divergence of ctenophore representatives. This protocol describes how to isolate genomic DNA from ctenophores. The procedure can be applied to adult tissues, but it is best to use embryos and larvae. After washing and concentrating the embryos or larvae, DNA is extracted using DNAzol reagent, a guanidine-detergent lysing solution. The resulting DNA can be used for polymerase chain reaction (PCR) or other applications.