Endometriosis is well established as a condition showing heritable tendencies. Polygenic/multifactorial etiology appears far more likely to be the etiology than Mendelian inheritance. The current task is to determine the number and location of genes responsible for endometriosis. This paper shall review the basis for concluding that endometriosis is a genetic disorder of polygenic/multifactorial inheritance and outline selected strategies for identifying the number and location of causative genes. It shall also illustrate our approach to testing the hypothesis that endometriosis bears similarity to neoplasia and, hence, is a multistep phenomenon of clonal origin.